I sometimes wonder if it's possible to use a gobo-linux style system, whereby the package manager just downloads the package to a versioned folder, possibly expanding it out, to a a package cache - then the venv need only symlink to it. The same could be done for python installs. Then do the same for the system python (e.g /bin/python points to /someplace/pyjunk/system/python, which in turn is a symlink to a particular interpreter, e.g. /someplace/pyjunk/interpreters/py2/2.7/cython_2.7_blub-i386/python).