generally, to slam someone down, you have to get rid of their connection between their legs and the ground. If you are implying that the marine is actually tripping the alien thus getting even CLOSER to the thing... well... then you be outside your mind, yo. but simply "pulling down" and not lifting and then slamming... well... not only would it look retarded, but it just wouldn't work ever. not even on a human.
@ yutani, I hope that is the case. kicking it off and shooting would be much more possible.