[Distutils] Upgrading eggs from custom url

[Charlie Moad]

     I am using setuptools to maintain some plugins I wrote for a
python based protein viewer.  I would like to have another plugin that
simply checks for updates for the currently installed plugins.  Code
may help, so basically I would like to run:

from setuptools.command import easy_install
easy_install.main('-U MyPlugin'.split())

This would work fine if I registered my plugins on Pypi, but just
trust me that I shouldn't be pushing this junk up there yet.  I saw
the "dependency_links" option, and that is close to what I want. 
However, I would also like easy_install to check for an update to
"MyPlugin" there as well.

When issuing an "--upgrade" option, can the "download_url" be checked
automatically, or is there an existing way I can get a handle on that
"download_url" variable to pass to easy_install?  Any advice would be
appreciated.

Thanks,
      Charlie