On multiple occasions I ended up pushing a Gurgle off screen with The Bean. Since they don't move forward after they start shooting, once they're off screen they just stay there and it's impossible to kill them without AOE attacks since babies can no longer target them.
I also think the Limited Edition challenge kinda sucks. I got stuck on it for about an hour before I decided to just not bother anymore. You have to get really lucky with enemy spawns to make it out of the early game because its basically a guaranteed game over if they decide to clump together in a single lane or body block each other in adjacent lanes, and as far as I can tell the Stoney near the end is impossible to kill unless he spawns in one of the middle lanes since I could never kill him even if I had as many Wiz Babies placed as I possibly could.