On PP&M's In Concert album, I believe it was Peter who introduced "Puff". He began by telling the audience that there would be those among them who would have a "wee, little voice" inside their heads which would say, "Sing! Sing!" "And," he said. "You're re-e-eally gonna want to sing. Please don't!"

I think there are many people who can't imagine that someone wouldn't want to have some backing for their song. I think they mean well (most of them - the rest are just trying to show off!). Perhaps addressing them in a humorous way as Peter did would work to get the message to them.