You could use a reciprocating saw with a bimetal blade. Stick the blade into the drain and cut a wedge out of the drain collar then pry it out. The trick here is to not cut the threads in the drain shoe which would present an entirely new set of problems. If you're not comfortable doing that you can also use a hacksaw blade instead of the recip. saw. It will take alot longer and you'll expend more energy, but sometimes "slow and steady wins the race".