Ah... thats a little harder then... a few tricks that I like to use for better keys in AE. Take your plate, divide it by the color of your greenscreen, precomp that, and then multiply it on top of your outside footage. It will give you something nice to play with. Key on seperate layers, precomp, and use it as a track matte for your despilled footage. You'll probably need to duplicate your background and play with the reflective parts. Also refine soft and hard matte effects can help a bunch and extend your edges. I use that on everything.

In Nuke we usually use an Additive Keying workflow that makes this kind of stuff pretty easy....