inhibit environment variable substitution in comint?

[Ralf Fassel]

I'd like to inhibit environment variable substitution in comint, since
the environment in the SHELL might be different from the one in emacs.

I.e. in emacs env(SRCDIR) is /usr/local/foo/
while in the SHELL it is /usr/local/bar/

The subdirectory layout etc is the same in both
  src/
  info/
  etc/

Now when I type TAB in the M-x shell buffer:
  % cd $SRCDIR/s[TAB]
emacs completes that to
  % cd /usr/local/foo/src
while I'd like it to complete to
  % cd $SRCDIR/src

(since SRCDIR in the SHELL is /usr/local/bar/, not /usr/local/foo/).

Looking at the sources im comint.el, it seems that
substitute-in-file-name is hardwired in many places, so there's no easy
way to disable it?

Any hints?
R'