Hyphenate typewriter / avoid overfull \hboxes in code, using fontspec and XeTeX

Question

I would like to avoid overfull \hboxes as a result of inline code, inserted with \textt{foo} or \ttfamily, e.g. in this MWE:

% compile with xelatex
\documentclass{article}
\usepackage[textwidth=4cm, showframe]{geometry}% to force hyphenation
\usepackage{polyglossia}
    \setdefaultlanguage[variant=usmax]{english}
\usepackage{fontspec}
    \setmonofont[Scale=MatchLowercase]{DejaVu Sans Mono}
\setlength{\overfullrule}{1mm}
\begin{document}
{\ttfamily Bla \textbackslash newcommand\{\textbackslash foo\}\{bar\}
\textbackslash setmonofont[Scale=MatchLowercase]\{DejaVu Sans Mono\}

For regular words, it works supercalifragilisticexpialidociously (or more like kind of ok),
but real code is tricky.}
\end{document}

I'd like to have hyphenation points (manual instruction is ok) between Match and Lowercase, and between {\foo} and {bar}. However, I don't ever want a hyphen to appear at hyphenation points (in typewriter text).

I've tried \-, which doesn't work (babelshorthands is not available for english). I also know about the fontspec option HyphenChar, but I don't know how to tell it "no hyphenation character, but hyphentation" (space / 32 is not an option because it appears in the OCR layer of the pdf; None would disable hyphenation altogether). I guess these might both be traces of the solution, but I can't figure out how to make use of them.

Answer 1

The first attempt uses a space character as hyphenation character, however I realized later that the OP explicitely had said it was a no-go. So there is a second attempt below which does not use the space (or other) character.

---

The following works with me (I commented out the DejaVu Sans Mono line as for some reason it does not work on my installation, tried to add ExternalLocation as option but this did not solve it and I don't use often enough XeTeX or LuaTeX to investigate further the reason of the problem)

% compile with xelatex
\documentclass{article}
\usepackage[textwidth=4cm, showframe]{geometry}% to force hyphenation
\usepackage{polyglossia}
    \setdefaultlanguage[variant=usmax]{english}
\usepackage{fontspec}
%    \setmonofont[Scale=MatchLowercase]{DejaVu Sans Mono}
\setlength{\overfullrule}{1mm}
\begin{document}
{\ttfamily\hyphenchar\font32 
Bla \textbackslash newcommand\{\textbackslash foo\}\-\{bar\}
\textbackslash setmonofont[Scale=\-Match\-Lowercase]\{DejaVu Sans Mono\}

For regular words, it works supercalifragilisticexpialidociously (or more like
kind of ok), but real code is tricky.}
\end{document}

Note that the space is used as hyphen character. And I added a few \- to the code.

---

I read now your 'space is not an option' it probably disqualifies my attempt! So here is a second try:

% compile with xelatex
\documentclass{article}
\usepackage[textwidth=4cm, showframe]{geometry}% to force hyphenation
\usepackage{polyglossia}
    \setdefaultlanguage[variant=usmax]{english}
\usepackage{fontspec}
%    \setmonofont[Scale=MatchLowercase]{DejaVu Sans Mono}
\setlength{\overfullrule}{1mm}
\begin{document}
{\ttfamily\def\-{\discretionary{}{}{}}%
Bla \textbackslash newcommand\{\textbackslash foo\}\-\{bar\}
\textbackslash setmonofont[Scale=\-Match\-Lowercase]\{DejaVu Sans Mono\}

For regular words, it works supercalifra\-gilisticexpialidociously (or more like
kind of ok), but real code is tricky.}
\end{document}

But I had to add explicitely a breaking point in the text part.