Wow, you've set yourself an absolute nightmare task. I spend most of my day cutting people from backdrops at the moment but I can't close on that (certainly can't do it at that resolution). The hair is almost every shade of grey on a backdrop that is likewise moves right through the grey spectrum. Not many would be able too do it.
Certainly I would think the solution won't be one method of masking. I imagine you are going to have to build up layers where different parts of the hair are visible and then composite. Honestly If I had something complicated I'd just mask it all out and paint the hair in by hand.