The following answer is a possible workaround (or a poor man's thread-bound Chinese book) using the PDF+LaTeX approach to Inkscape and pdflatex. Some parts of it, if not all, can probably be adapted to xelatex.
One strategy to solve the issue of text alignment in Inkscape is to use zero-width \makebox boxes in combination with \colorbox and \raisebox commands, since the contents of LR (left-right) boxes can be arbitrarily complex [The LaTeX Companion, p. 860].
preamble
The new declarations you need depend on the problem at hand. Although I'm unfamiliar with Mongolian and Manju (and what exactly are the language requirements to recreate a thread-bound Chinese book), I had a look at the montex manual and defined three new commands, \ibox, \icbox and \ipbox.
\documentclass{article}
\usepackage{calc}
\usepackage{graphicx}
\usepackage[dvipsnames]{xcolor}
\usepackage[latin1]{mls}
%% LR-box and paragraph box commands to lay text in Inkscape
%%
%% LR-box: #1 = (optional) value of \fboxsep
%% #2 = horizontal alignment relative to anchor, [c], [s], [l], [r]
%% #3 = text
\newcommand{\ibox}[3][0mm]{{\setlength{\fboxsep}{#1}%
\makebox[0pt][#2]{\raisebox{-1.0\height}[0pt]{\colorbox{White}{#3}}}}}
\newcommand{\icbox}[3][0mm]{{\setlength{\fboxsep}{#1}%
\makebox[0pt][#2]{\raisebox{0.5\width}[0pt]{\colorbox{White}{#3}}}}}
%%
%% paragraph box: #1 = (optional) value of \fboxsep
%% #2 = horizontal alignment relative to anchor, [c], [s], [l], [r]
%% #3 = height above anchor as a fraction of box height
%% #4 = text
\newcommand{\ipbox}[4][0mm]{{\setlength{\fboxsep}{#1}%
\makebox[0pt][#2]{\raisebox{#3\totalheight - 1.0\totalheight}[0pt]{\colorbox{White}{#4}}}}}
The first two commands, \ibox and \icbox, are ideally suited for the following montex commands:
\bosoo
\mbosoo
\mobosoo
\mabosoo
The first argument of both commands is optional, whilst the second argument controls horizontal text alignment relative to the object anchor (in Inkscape): [l] makes text stick out to the right; [c] centres it; [r] makes text stick out to the left. The only difference between the two commands is that \ibox lays text below the object anchor, whilst \icbox centres the text vertically relative to it.
\ipbox is better suited for vertical text boxes constructed with \mobox or \mabox. The first argument is optional, and the third argument is used to control vertical alignment of the box about the anchor,
\ipbox{...}{<value>}{...}
where <value> is a fraction of the total box height, so:
<value> = 0 lays text below the anchor
<value> = 0.5 centres text vertically
<value> = 1.0 lays text above the anchor
patch for Inkscape (optional)
The PDF+LaTeX option generates two files with extensions .pdf and .pdf_tex. If you have many files, re-exporting all SVG files to PDF becomes time consuming. Below you'll find a patch for Inkscape (add it to your preamble), so that when you modify one of your SVG files, running pdflatex on your main .tex file will cause Inkscape to re-export that SVG file to PDF automatically.
\usepackage{import} % provides \import and \subimport to establish
% input relative to a directory
%% Inkscape patch that re-exports <file>.svg to PDF+LaTeX in Inkscape
%% whenever the SVG file is updated
%% NOTE: the current patch requires that all three files (i.e., .PDF,
%% .PDF_TEX, and .SVG) have the same name and be present in the
%% same directory
%%
%% modified from:
%% http://anorien.csc.warwick.ac.uk/mirrors/CTAN/info/svg-inkscape/InkscapePDFLaTeX.pdf
%%
%% \executeiffilenewer compares the modification date of SVG and PDF files
\newcommand{\executeiffilenewer}[3]{%
\ifnum\pdfstrcmp%
{\pdffilemoddate{#1}}%
{\pdffilemoddate{#2}}%
>0%
{\immediate\write18{#3}}%
\fi%
}
%% \includesvg is used to include graphics
%% syntax: \includesvg{<file>}, \includesvg[path/to/file/]{<file>}
\newcommand{\includesvg}[2][]{%
\executeiffilenewer{#1#2.svg}{#1#2.pdf}%
{inkscape -z -D --file=#1#2.svg --export-pdf=#1#2.pdf --export-latex}%
\subimport{#1}{#2.pdf_tex}%
}
For the patch to work you'll need to (1) add Inkscape to the search path of your operating system and (2) pass the command line argument -shell-escape (or perhaps --shell-escape) to the pdflatex compiler. The latter depends on your settings: operating system and editor. You'll find instructions for Texmaker (or TeXStudio) here, and for TeXworks (on Windows) here (see step 2).
the Inkscape environment
Here's a screenshot of how I included text objects in Inkscape:
- The red circle indicates the anchor position of that text object. The anchor position is controlled in Inkscape by the setting the type of text alignment (left, center, right). It determines the point relative to which text is to be placed by
\ibox, etc..
- Yellow, dashed lines are auxiliary lines for text alignment (saved to another layer on Inkscape). Anchor of text objects is aligned with these lines.
- Font size on Inkscape has no effect on final result.
- Ensure Inkscape's bounding box sits tightly around the main frame (it's ok if some text objects stick out of the frame). One way to do it: select the entire drawing except(!) for the text objects, then go to Document Properties, Resize page to content, and click on Resize page to drawing or selection.

Included strings (from top to bottom, left to right):
\ibox{c}{\LARGE\mabosoo{uindur}}
\ibox{c}{\small\mabosoo{uindur gegen}}
\ibox{c}{\small\mabosoo{zanabazar}}
\ibox{c}{\Large\mabosoo{ugar}}
\ibox{c}{\large\mabosoo{17..18 ugar zagun-u}}
\ipbox{c}{0.5}{\mobox{3.75cm}{%
\noindent\raggedleft
cinggis xagan-u aldan urug-un izagur surbulzidan abadai
saiin nuyan xan-u kuiu}}
File saved as cnbook.svg, and then exported to PDF with option PDF+LaTeX (saved as cnbook.pdf). You can download a copy of these files here.
inclusion of graphics in LaTeX
For including graphics without the patch, place a copy of all three Inkscape files in the same directory as your main .tex file. Then use:
\begin{document}
\large
\begin{figure}[h!]\centering
%\def\svgwidth{<desired width>} % \svgwidth is forgotten outside the figure environment
\input{cnbook.pdf_tex}
\end{figure}
\end{document}
For including graphics with the patch, replace \input by \includesvg. For example, if you place a copy of all three Inkscape files in a child folder graphics, then use
\includesvg[graphics/]{cnbook}
End result:

vertical display of CJK characters
The solution is to place \rotatebox inside the argument of \ibox (not the other way around). However, this command was declared with Mongolian and Manju in mind, so you may need to tweak it for other languages. For Chinese characters in the Ming typeface \ibox may look a bit odd, consider:
%% compiler: xelatex
\usepackage{graphicx}
\usepackage{rotating}
\usepackage[dvipsnames]{xcolor}
\usepackage{fontspec}
\usepackage{xeCJK}
\setCJKmainfont[RawFeature={vertical}]{宋体}
%% same as before
\newcommand{\ibox}[3][0mm]{{\setlength{\fboxsep}{#1}%
\makebox[0pt][#2]{\raisebox{-1.0\height}[0pt]{\colorbox{Yellow}{#3}}}}}
%%
%% LR-box: #1 = (optional) value of \fboxsep
%% #2 = horizontal position relative to anchor
%% #3 = height above anchor as a fraction of box height
%% #4 = text
\newcommand{\icjk}[4][0mm]{{\setlength{\fboxsep}{#1}%
\makebox[0pt][c]{\raisebox{#3\totalheight}{\rotatebox{-90}{\raisebox{#2}[0pt]{#4}}}}}}
\begin{document}
aaaM\ibox{c}{\rotatebox{-90}{latin}}%
aaaM\ibox{c}{\rotatebox{-90}{大清全書}}%
aaaM\icjk{0pt}{0}{大清全書}%
aaa
\end{document}

With \icjk, you can control easily the horizontal and vertical alignment of the characters:
\icjk{0pt}{0}{大清全書}\rule{1cm}{0.5pt}
\icjk{0pt}{0.5}{大清全書}\rule{1cm}{0.5pt}
\icjk{0pt}{1.0}{大清全書}

Inkscape screenshot next to PDF output:
\icjk{0pt}{0.5}{\Huge{}大清全書} % first column
\icjk{0pt}{0}{\LARGE{}大清全書} % second column

pdlatexcompiler is called by default, notxelatex. In order to use the latter, changes to the filetextext.py(which can be found in\Inkscape\share\extensions) would probably be necessary. Also, have you considered exporting graphics to a PDF with all the text put into a.texfile as opposed to using TeX Text? There are various advantages to the PDF+LaTeX approach. – nnunes Jan 28 '13 at 03:10xelatex. However, I can't find the filetextext.pyusinglocatein the Mac OS terminal. I installed Inkscape throughmacports; is the file located somewhere else? As for the PDF+LaTeX approach, I have tried it, but it's difficult to get the Manchu text to align properly, since the output will look very different from the command\bithe{TEXT}. What I want to do is to build pages that look like this: http://db.tt/fwitsmQc (I don't have Adobe Indesign, which people usually use for this kind of stuff, as in: http://tinyurl.com/b8vy7yg) – Mårten Jan 28 '13 at 14:49textext.pyin~/.inkscape/extensions/or~/.inkscape/extensions/textext-0.4.4. I can call thexelatexcompiler by modifying line 730 oftextext.py, but TeX Text will complain iffontspecis loaded. – nnunes Jan 28 '13 at 23:53