You said he's gotten farther into the can... that implies his body is thin enough to fit in the hole... I think you should just take a can opener, a serrated knife, or a big saw and cut the very end of the can off. (the bottom, the end opposite the end he's stuck in...) He will back his head away when he sees the blade cutting in, I'd imagine. He MIGHT strike at you, but I doubt it... besides, someone already pointed out he's harmless.
Stop trying to get his head OUT of the can, and instead open the other end of the can for him. Basically.