Okay, it's not actually cake-powered, but it does use cake!
Owing to the fact that cake and trapdoors are less than half a block tall, we can use fenceposts (which are a block and a half tall) attached to pistons to push people along, because the tops of the fenceposts will invisibly pop up through cake and trapdoors.
Here's a cool video of it in action:
So come to our workshop this Saturday, August 4th at 12:01 pm PST (3:01 pm EST) on our Minecraft server, mc.wonderhowto.com in order to participate!
You'll get the most out of the workshop if you join our Teamspeak server, ts.wonderhowto.com, so load it up and drop on by!
I look forward to seeing you there!