Real Shadows in CG Environment

I’ve been looking for a way to get the shadows of actors/physical set components into a CG environment, short of creating models of them and casting shadows from those.

Does anyone know a good way to do it?

Unless the shadows were cast into a scene specifically set up for keying and shadow separation, it’s really not going to be possible. It would be much easier to fake it with 3D modeled props and characters than to try and extract shadow data from a random shot.