You would have to work with khan, who would host the online game and as people fulfilled study milestones they would get a period of game access. This game could be on the same iPad that the pupil studied on. Probably minimum game times of 20-30 minutes of play for whatever milestone the pupil reached.
Each course would need a game that suited the academic level of the pupil. I suspect game companies would be eager to fill this need, as long as some sort of monetization method could be setup? I know Khan Academy = free, but are there games fueled by advertising that would fit?
The idea of paying pupils to study is a very valid and worthwhile method of motivation of pupils. Toss out the judeo-christian crap that overlies our minds and we can see that rewards motivate people. Who works for free? Study is work - pay them