I simply say "Nothing stupid, guys" and I set up about 5 yards deep instead of 15. As soon as the knee starts to the ground, I make sure my whistle is in my mouth.
I haven't had anyone fake it yet, but sounds like a good time for an inadvertent whistle. (Note the
here. Not sure if this means I'm kidding or I'm tweaking those who think preventing bad behavior at the end of a blowout is a terrible idea.)