row machine is out, cause your gonna feel your hams for sure.
heavy bag work, speedbag work, and even shadowboxing. i usually do 3 min on 1 min rest... and take make shadow boxing more work, you can use a light weight... your shoulders will get hammered for sure.
also, skipping rope might be a good idea. a good rope skip mostly bounces on the toes, and wont engage your hams much.. try it out. ITS ALL ABOUT THE JUMP ROPE.