This thing needs some sort of conclusion. They lined up these boys in the beginning as if it was some sort of casting. So, obviously there's something to win. Maybe the cheerleader club was looking for a boy mascot or something.

Something prestigious enough for all the boys to be willing to lose their balls for.

So whoever that last boy is, he needs to

a) prove himself to them and

b) get some sort of reward.

I think b should definitely not be "buttfucking" - although a) could include that. Maybe the last one is sent to fuck all the previously "modified boys" and when he can do that satisfactorily, he gets a reward:

1. he gets to keep his junk
2. the girls get to keep him (he obviously has enough stamina for the job) and can give them some well earned relief after cheerleading session
ending scene could show them all lined up, legs spread and he is dutifully giving one after the other some cunnilingus ;)

but what to do with the "cast offs"?

well, ill leave that open for discussion. we do need more gore here, so maybe some kind of fun last-boy-standing deathmatch which the girls spice up by firing darts and other sharpies at them ;)