By "back" I mean the small room in the end of the hallway next to the harpoon. All the mobs spawn there. I reset the boss once after safely collecting 6 harpoons and then run all the way back there before he respawns. Then one shammy runs back to start the event while the others AOE down the initial mobs. The puller shammy joins in once he gets back there. Then I wait until the mobs are somewhat cleared (new ones spawn all the time) and shoot the boss down when he passes. I've only succeeded this one time though but I intend to get another kill later tonight.