Have him stand in the middle of the room, on top of the platform where the bosses originally start. He should be able to outrange the auras there. If he isnt, he is doing something wrong. Also, your ranged dps does not have to stand right on top of the bosses. Have them stay closer to the center so your healer does not have to get off the platform.
For 25man, I would recomend 2 healers on that side at a minimum.