Mecanim animation clip mask

Hello, I'm using Mecanim in Unity 4.1.2f1. I am wondering how to use body and transform masks for animation clip (not for animation layer). Can I set per-bone mask? Or it wold be overrided by bodymask all the same? I mean, for example, the situation when body mask for animation clip wold be only legs, but to choose only lower part of legs in transform mask? Thanks in advance.