Ah, so as I suspected (but too lazy to re-check the disassembly), oh-noers are not affected by the behavior I referred to. That's incidentally exactly why I said "I'm not sure" instead of flat out saying it's impossible.
Good job for working out a solution though.
Maybe the low save percentage made it possible to get something working without too much trial and error?
Anyway, turns out Steve has a good idea I think in terms of terrain, just the wrong approach as far as skills are concerned. Here's my level, inspired by his, that should satisfy your challenge. In fact I almost think I might've "backrouted" your challenge by doing what I did......
Oh, and busy-ness and other considerations say I'll call open floor yet again if my level works.