I used to work for a man who had a very helpful and effective technique. When I was doing something wrong, he would say, "I need you to..." and then he would say what was the right thing to do.

In this case, the performer should stop dead in the middle of a song, look at the perps and say "I need you to stop recording this concert."

For one thing, the performer has authority that nobody else has. For another, the social pressure on a person who has caused the whole show to slam to a stop is tremendous. I think it's well worth trying.

(I know a priest who stops talking when a baby cries. Usually a baby cries for only a few seconds, and nobody minds. But if the baby fussed and fussed, the cessations would soon drive the most pig-headed parent to remove the kid.)

By the way, somebody said this behavior is illegal, but is it?