I'm guessing the biggest challenge in that idea would be getting hold of Hammerhead, since you can't use normal pickaxes, you can't use wands of digging, and, since Soirana is talking about using an assassin, you can't kick down walls. So unless Soirana is allowed to pick up a spellbook for long enough to read it and get Mystic Shovel (which would be hard enough to read as an assassin, I'm assuming), Hammerhead would be the only way to reasonably get into the temples.
Or am I mistaken?
So far rolled 15 casters with RoDS and shamelessly killed them within 200 turns. For eternium glory!
(after 15 I stopped counting...)