Alright, I've got some rough ideas. Tell me how this sounds:
+1 rebate power, modifies a number of other powers.
You can store a number of "charges" equal to three times the total cost of the powers modified.
Using a power for an action costs charges equal to the refresh cost.
Recharging is fairly easy under normal circumstances, but too slow to work during combat and occasionally not possible for whatever reason.
If recharging is not easy under normal circumstances, further +1 rebate.
If you have multiple powers, you can make them require different fuels. This means that you get multiple types of charge, one for each (group of) power(s). +2 rebate for 3 different fuels and +3 rebate for 8 different fuels. You can still only carry a total number of charges equal to 3x the total cost, so split them up carefully.