i agree, sumo deads are good.
leg ext with some nice 5 second squeezes. lunges will hit the ass but also the hams really well.
one question? is your ass getting too big musclewise? or do you need to lean out? (not being a dick, just trying to narrow down the actual reason for avoiding squats.) if you could stand to lean out, chances are your ass isnt growing THAT big, it just means the winter coat is accentuating the muscle beneath. squats are phenomenal for leg mass, if you are going ATF, then you might want to rethink it and go just to parallel. ATF tends to bring out a bit more glute involvement, hence the term "squatters ass". hacks would be good too, but depending on how far you move your feet forward, will determine the amount of glute involvement, at the same time the further back your feet go, the more stress your knees will get. double edge sword.