[Kelly Pedersen]

For allowing someone to "overflow" their normal FP with this, I'd build that as an Affliction Linked to the Healing, afflicting them with Energy Reserve with the "Special Recharge" limitation, specifying that it can only be "charged" by energy provided by the Healing. That's about +9% per level of ER you're adding, so it's actually not too expensive as an enhancement on Affliction.