Sounds like toe-in, toe-out is your problem. If they look pigeon-toed, that is. Camber is the way the tire leans from vertical. I don't see why you can't change the toe on the car. I would get a second opinion from another mechanic. Try to find one versed in the rear suspension. There are a lot of things that can be moved around on your rear suspension as it is.
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.