Yup, after killing Margoth i saved up all my AP to dash back into the room everytime i went out and moved a chair/took a shot or cast a spell. I had three spellcasters though, so i was casting boulderbash/small fireball/blitz bolt and ice shard regularly and doing a good 300 damage each turn to a demon.
It took me a really long time to do it this way. Once i was down to two demons i charged my 2h warrior out and stomped on the fiery demon with the rest supporting her and drawing a bit of aggro from the other.
Make sure you are regularly healing, if you have the companion mage just keep spamming healing whenever he has a bit of spare AP on whoevers most likely to take damage next.
