compoze does the latter part (fetching source distributions corresponding to the
current
working set, building a PyPI "simple" index from them).  The bit about keeping the
source dists is not going to happen.

By default, setuptools will discard source distributions which it downloads
after using
them to build and install a binary egg.  For repoze.project, we should figure
out how
to do the followng:

 - Instead of downloading them into t tmpdir, put them into the 'src' directory
   (or something) of the virtualenv.  It should still be able to unpack into a
   tmpdir.

 - Prevent setuptools from deleting the tarball after unpacking it.

If we do this, we can then introspect 'easy_install.pth' to get the
"known good set" for the virtualenv, and even generate a
"package index in a box" from it.