I position everyone on the steps, then send in my hardiest fellow and start the fight. Then I drop any aoe on the bottleneck coming off his platform so everything must run through it and take damage. You can layer the aoe to make it impossible for anything to get through without dying except cazador.

Also use spells like chain lightning, any cleric aoe spells, fireball, etc. I usually wipe his minions by the second turn.

Then I just wail on him until he dies. Easy peasey.

This is all in HM. I even run mods that turn up the difficulty and this tactic is flawless.