Let me start by saying, that I don\'t think there is a way to do this... but, there are a lot of clever people out there and so I thought I would ask! :)
I found a
I had similar needs in buildout and implemented it there. Now that I am migrating from buildout to pip, I came out with this script to use some various requirements files based on some conditions, that can based on os/arch or some environment variable or anything you like. Crude but effective for me.
See https://gist.github.com/pombredanne/72130ee6f202e89c13bb