I am trying to add a path to the PYTHONPATH environment variable, that would be only visible from a particular virtualenv environment.
I tried SET PYTHONPATH=
You can also try to put symlink to one of your virtualenv.
eg. 1) activate your virtualenv 2) run python 3) import sys and check sys.path 4) you will find python search path there. Choose one of those (eg. site-packages) 5) go there and create symlink to your package like: ln -s path-to-your-package name-with-which-you'll-be-importing
That way you should be able to import it even without activating your virtualenv. Simply try: path-to-your-virtualenv-folder/bin/python and import your package.