He scenes need a few guys cumming in the girl's mouth not only at the end of the movie, but also at the beginning and in the middle.
The idea would be like this:
2 or 3 guys cum in the girl's mouth as a startup, just like in the vampires resurrection movie, or like the clockwork gang bang, but instead of the mysterious medicine, it is the actual cum swallow which turns the girl on.
Then the gang bang starts, usual stuff, could be a 5 on 1, dp,dap etc. While the girl is in the middle of the action, time to time, a new guy enters and leaves his load in the mouth. Without stopping fucking, she swallows and continue the scene. This should happen 3-5 times while the girl is dp'ed or dap'ed.
Then usual final as always, the guys finish in the girls mouth being in a round or in the sofa.
This could use th 10 man gangbang or 12 in 1 guys.