Do what I do as tank, and tell your healer (and group in general) to stay close to you, don't run around a lot, and then you can really easily pull spirits off the healer with AOE moves. When the spirits are one at a time they can just be dpsed down by the ranged no problem, but when a big bunch come at once it's usually best to group up and let them be tanked till they're dead, then continue.
It's all just about control. I've not had any big problems with pugs on that boss, I just tell everyone stick close to me, kill the big add after first bodyslam, it becomes a very easygoing fight.