@Ben Stiegler The group, and the manager of their venue, tried:
A cue light, a Clear Com handset the (type that's listen only 'til you squeeze the grip) AND stationing an experienced usher
(who'd been ush'ing the production for a week or more and all too well understood the importance of not opening the doors too soon)
immediately inside the double doors of the auditorium intent on keeping the doors closed until the house lights began their 3 second fade up.
All to practically no avail; the instant the House Manager heard the first clap of applause she'd begin hauling on the doors like she was hauling a molester off her mother's back; it would've taken chains 'n locks cinched tightly around the crash bars to slow the HM down 'n ya gotta know the Fire Marshal'd frown at the sight.
Some people are just too (dumb / bull-headed / ignorant) to (train / employ / trust / reason with) [Insert your choices of terms )
Toodleoo! Pavlov had better luck with his dogs.
Ron Hebbard
One only needed a bell to ring and some puppy kibble... but sometimes you just have to have the head usher take the HM off to the side with "a really important problem only YOU can fix..." Then ring the bell and toss them the dog treats.