That only works because football and soccer share one of the dumbest rules in any sport:
The clock keeps running even after the whistle is blown and the play is dead.
Play football in four 5-minute quarters, and stop the clock EVERY TIME the whistle blows at the end of a play.
Do it like soccer. Don’t let them know how much time is left in a half, I think the CFL used to do that at one time.