i definitely remember having mp problems in groups that didnt move out of poison fast
but can't you view your healers mp bar in your window..

get your friend to take him to the outskirts of the room facing one way, with ranged dps/healer sat behind his back but not quite on top of each other, whenever he turns round to spit, tank moves a few steps around the outskirt of the room and everyone follows, he should be dead by the time you've done a circle of the room and if he isn't the poison pools start disappearing then so you can do a second lap