Why not just make the damn spell activate like a Death & Decay? You cast it in an area and it heals whoever is ontop of it for a certain amount and lasts a certain amount of time until it runs out, something like:
Places a Well of Light in an area causing friendly targets on the Well to be healed for x amount every 1 second for 12 seconds. When Well of Lights duration ends, it explodes causing nearby targets to be healed for x% amount of total healing done. 3 Minute Cooldown.
Or something, maybe have it do Holy Damage as well to add to overall dps of a raid, if used on melee targets it could be pretty powerful if underneath a boss, depending on how well it scales.