i was going to suggest this myself, but i have a bit of a different idea. on that map there is a cave with the poison creature (whatever it's called, i haven't had my coffee yet) and the web trap. why don't you change it so that when you walk in there it looks like the cave from the gnoll stronghold (perhaps mirrored so it's a bit different) and fill it with xvarts ... better yet, maybe you could use the map from the undead village in the bottom of the unseeing eye pit and make it like a separate mini xvart village in a cave.