Easy, go into the dungeon (just till you see the red text "Rahz Inkur"), pull some mobs and pull them back to where you came and go outside the dungeon and voilá, all the mobs you pulled are immobile at the dungeon border. Now you can kill them with ranged skills/spells/pets
With outside the dungeon I mean when you're not inside the Rahz Inkur dungeon area.