Monroville said:

Keep in mind Vader doesn't throw anything at the carbonite control lever when Luke falls into the carbonite pit (so if Vader is shown flipping a switch with the force, can't Luke do it after a few years of practice?).

I could see deleting the rock/skull/whatever, show Luke pointing at the door with a nice "green to red" or just set of light switches to indicate it's closing, and then show the door closing at an increased rate of speed (slow at first, then speeding up and slamming down on the Rancor's head). Even implying Luke is not even activating the switch, but using the force to bring the door down would add to Luke's cred as a near-master.

My thoughts exactly.