With the contest I was in, the judges were not on stage with us, their table was off stage, off to one side. So you would walk past them after you had had your stage time. And last year, the judges were sitting on stage, but they were sitting on the same side of the stage as we entered from, so it was possible to walk past them, bow (completely in-character), and hand them my notes before going out to the middle of the stage to do my thing. (there was no pre-judging there)
After that first contest, I did post my complaints to the con forum. But I did so constructively, offering ideas for ways to make the next contest better. And it looks like con staff really do care, aiming to make it better for us every year.