How can I install the python bindings into a virtualenv?

[Michel Albert]

I am currently dipping my feet into gstreamer for a python project. I
have my pipeline properly set up and tested using gst-launch.

Now I want to add it to my python project, but as the python bindings
are not using the standard python installation procedure, I don't know
how I should install them. Has anyone some experience with this?

I want to avoid "opening up" my virtualenv with the "--system-site-packages"