The MJ 'thrust" I remember has him rise up on his toes. That means EVERYTHING on his body MUST move, so IK probably won't help anyway. Assuming his feet are close together, I'd do 1 static pose in the standing position, save it, zero the figure, then do a second pose in the thrust position, save that, and just do a 5 frame animation with your figure at pose 1 for frame 1, pose 2 for frame 5, and let Poser do the tweening. You only really need to ensure the feet are in the right positions, but that can easily be tweaked. This will work for all his moves, including the thrust and hat grab. Just make sure the feet are touching the ground and not sliding too far.