IP locking with freeradius

HI Everyone! There is something I am trying to do with radius and can't find how. (One month googling and nothing done...) What I want is to authenticate my users with their MAC and IP-ADDRESS, so, even if they have root-access to their systems, they can't change their IP-ADDRESS by themselves, because radius is going to reject then. Until now, I have a radius mac-authenticating and working together with dhcpd. I've tried to use ip-pool, that works, but someone still can change ip-address by hand and keep networking.... So, it is possible to work this out? Thanks