I have a fresh install of python 2.6.4 in /opt/py26/ installed as root. As root I now also install the lockfile module with
$ /opt/py26/bin/python setup.py install
As user I create a virtualenv with
/opt/py26/bin/python virtualenv.py ~/py26 --distribute
Now I run
which tries to download the lockfile module and installs it in my virtualenv. If I remove the --distribute option, setuptools recognizes the old installation of the lockfile module in /opt/py26/... and does not reinstall it.