I think I found an easy skip in Alternative Means of Transport. I was trying to figure out how to get Jeff in this stage (still doing my casual playthrough) and found that if I hit this spot with the cannon and mash jump while doing so, the player/corpse jumps and hits the goal, finishing the level.

EDIT: I played around with it a bit more and you don't even need to jump when hitting the ceiling, the bounce off that surface is just weird.