Holy Spirit Bomb - Summons a Holy Spirit Bomb which can be filled with holy light (heals) up to <amount here>. The Holy Spirit Bomb has 30,000 health and will detonate upon being destroyed, healing all members in the party/raid for <amount here>. 2 minute cooldown.
Basically the idea is after Holy Spirit Bomb is cast, healers have to fill it up using heals, then dps in the raid can detonate it to heal the raid at an opportune moment or when needed. Not a full heal all around, but something large enough to make it a useful part of raiding.