Are your flies escaping when you are putting them in a dust cup? I usually only get mass escapees when in not careful when transferring flies from cultures to a dust cup.

I do get some rogue flies that escape the vivariums but not enough to be a problem.

Some people set up "feeding stations" in their tanks by placing a slice of banana for the flies to congregate... I don't do this though... I want my frogs to hunt for their food.

My frog room is my bedroom and I have 13 vivariums all containing dart frogs. I like to vacuum after feeding to catch any flies that escaped during feeding.