Wow, his use of the cat to get the silver trophy was brilliant.
My solution was the same as yours. I'd like to present my own challenge, however! Can you get the Vault ending by only unlocking two doors (period) and without entering the village? (Obviously no cheat code or developer mode allowed.)
It might be best to make a separate thread for that to avoid making things too cluttered.
I'll give your challenge a shot later, but I'm currently doing the finishing touches on one of my own. I think I already have a vague idea of what I'll have to do for yours though.
BTW, games here normally get a sub-forum for challenges. Could a mod create one for Uurnog and move this topic there?