Note See the GhostChapters version at the bottom
The preliminary entries can be added by faking \addtocontents and omitting the 2nd argument to the original \contentsline{} command, thus removing the page number.
In lack of a MWE this works for book, scrbook and memoir classes so far only.
\documentclass{book}
\usepackage{etoolbox}%
\newcommand{\addfakecontent}[2]{%
\refstepcounter{#1}%
\addtocontents{toc}{\protect\contentsline{#1}{\csuse{the#1}\hspace{1em}#2}{}}
}%
\AtEndDocument{%
\addfakecontent{part}{The next to final part}
\addfakecontent{chapter}{Some chapter of another part}%
\addfakecontent{chapter}{Even another chapter of another part}%
\addfakecontent{part}{The final part}
\addfakecontent{chapter}{Some chapter of the final part}
\addfakecontent{section}{A section of a final part}
}
\usepackage{blindtext}
\begin{document}
\tableofcontents
\part{First}
\chapter{Some chapter content}
\blindtext
\end{document}

Ghostchapter - version
This version uses the concept of ghost chapters (i.e. \parts, \chapters etc.) By using \EnableGhostChapters at 'any' arbitrary position in the document the following structure commands are disabled, but add an entry to ToC. It works for scrbook, memoir down to subparagraph, and up to subsubsection for book class -- I did not figure out why it fails for paragraph and subparagraph for the book class... (weird definition?)
The ghost chapters are displayed with darkgray color in the ToC.
Use \DisableGhostChapters to switch back to normal behaviour.
The macros \EnablePagesInToc and \DisablePagesInToc enable/disable the display of the page number in the ToC
Note: Although I used \patchcmd ... it's not a patch, it's a hack ;-)
It does not work correctly for \include{} but with \input{}
\documentclass{book}
\usepackage{xcolor}%
\usepackage{etoolbox}%
\newcommand{\preliminarycontentscolor}{darkgray}
\newbool{UsePagesInToc}
\newbool{GhostChapters}
\newcommand{\EnablePagesInToc}{%
\clearpage
\setbool{UsePagesInToc}{true}%
}%
\newcommand{\DisablePagesInToc}{%
\setbool{UsePagesInToc}{false}%
}%
\newcommand{\EnableGhostChapters}{%
\DisablePagesInToc%
\setbool{GhostChapters}{true}%
}%
\newcommand{\DisableGhostChapters}{%
\EnablePagesInToc%
\setbool{GhostChapters}{false}%
}%
\setcounter{tocdepth}{5}
\setcounter{secnumdepth}{5}
\makeatletter
\def\addcontentsline#1#2#3{%
\ifbool{UsePagesInToc}{%
\addtocontents{#1}{\protect\contentsline{#2}{#3}{\thepage}}%
}{%
\addtocontents{#1}{\begingroup\color{\preliminarycontentscolor}{\protect\contentsline{#2}{#3}{}}\endgroup}
}%
}%
\makeatletter
\patchcmd{\@part}{%
\markboth{}{}%
{\centering
\interlinepenalty \@M
\normalfont
\ifnum \c@secnumdepth >-2\relax
\huge\bfseries \partname\nobreakspace\thepart%
\par
\vskip 20\p@
\fi
\Huge \bfseries #2\par}%
\@endpart%
}{%
\ifbool{GhostChapters}{\thispagestyle{empty}}{%
\markboth{}{}%
{\centering
\interlinepenalty \@M
\normalfont
\ifnum \c@secnumdepth >-2\relax
\huge\bfseries \partname\nobreakspace\thepart%
\par
\vskip 20\p@
\fi
\Huge \bfseries #2\par}%
\@endpart%
}%
}{\typeout{part structure successfully patched}}{\typeout{part structure patching failed}}
\patchcmd{\@chapter}{\chaptermark{#1}%
\addtocontents{lof}{\protect\addvspace{10\p@}}%
\addtocontents{lot}{\protect\addvspace{10\p@}}%
\if@twocolumn
\@topnewpage[\@makechapterhead{#2}]%
\else
\@makechapterhead{#2}%
\@afterheading
\fi}{% Patch
\ifbool{GhostChapters}{\thispagestyle{empty}}{%
\chaptermark{#1}%
\addtocontents{lof}{\protect\addvspace{10\p@}}%
\addtocontents{lot}{\protect\addvspace{10\p@}}%
\if@twocolumn
\@topnewpage[\@makechapterhead{#2}]%
\else
\@makechapterhead{#2}%
\@afterheading
\fi}
}{\typeout{chapter structure successfully patched}}{\typeout{chapter structure patching failed}}
\patchcmd{\@sect}{%
\ifdim \@tempskipa>\z@
\begingroup
#6{%
\@hangfrom{\hskip #3\relax\@svsec}%
\interlinepenalty \@M #8\@@par}%
\endgroup
\csname #1mark\endcsname{#7}%
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}%
\else
\def\@svsechd{%
#6{\hskip #3\relax
\@svsec #8}%
\csname #1mark\endcsname{#7}%
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}}%
\fi
\@xsect{#5}}{%
\ifbool{GhostChapters}{%
\ifdim \@tempskipa>\z@
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}
\else
\def\@svsechd{%
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}}%
\fi%
\@xsect{#5}%
}{%
\ifdim \@tempskipa>\z@
\begingroup
#6{%
\@hangfrom{\hskip #3\relax\@svsec}%
\interlinepenalty \@M #8\@@par}%
\endgroup
\csname #1mark\endcsname{#7}%
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}%
\else
\def\@svsechd{%
#6{\hskip #3\relax
\@svsec #8}%
\csname #1mark\endcsname{#7}%
\addcontentsline{toc}{#1}{%
\ifnum #2>\c@secnumdepth \else
\protect\numberline{\csname the#1\endcsname}%
\fi
#7}}%
\fi
\@xsect{#5}
}%
}{\typeout{section structures successfully patched}}{\typeout{section structures patching failed}}
\AtBeginDocument{%
\DisableGhostChapters%
\EnablePagesInToc%
}%
\AtEndDocument{%
\phantom{some output}
}%
\makeatother
\usepackage{blindtext}
\begin{document}
\DisableGhostChapters
\tableofcontents
\part{First}
\chapter{First of first part}
\section{First section of first chapter}
\subsection{First subsection}
\subsubsection{First subsubsection}
\paragraph{First paragraph}
\subparagraph{First subparagraph}
\blindtext
\chapter{Second chapter}
\EnableGhostChapters
\part{OtherOne}
\chapter{New Chapter}
\section{Section of another chapter}%
\chapter{Another chapter}
\chapter{Yet another chapter of another part}
\section{First section of another chapter}
\subsection{First subsection}
\subsubsection{First subsubsection}
\paragraph{First paragraph}
\subparagraph{First subparagraph}
\EnablePagesInToc
\DisableGhostChapters
\chapter{You will see me!}
\part{And some visible part}
\EnableGhostChapters%
\DisablePagesInToc%
\chapter{With an invisible chapter}
\end{document}

\addcontentsline{toc}{part}{theverysophisticatedtitle}etc, but this is tedious and won't update the corresponding numbers. Should the titles be 'correct' already or are dummy titles sufficient? – Nov 03 '14 at 15:59emptychapters etc, doing nothing, perhaps with a boolean state variable – Nov 03 '14 at 16:57\includepdfto just grab the first part - i wasn't sure though whetherhyperreflinks would break or not. – Christian Ivicevic Nov 03 '14 at 17:04