Offering them food =/= power feeding.
Power feeding is cramming another mouse/rat into a ball's mouth as they are just finishing swallowing the first one (or second, or so on).
I OFFER my balls as much as they want, once a week. They typically will not overeat. If they eat a little much, they don't eat the next week.
After a 6+ month period off feed I'd offer as much food as the OP too.