Even if the OP is doing it at an anime convention, he should be ok. ...That being said, you should seek sensei's permission AND determine the intent of the convention organizers.
i apologize if i was unclear, but i am in no way in charge of the decision to put this demo on, and i am not a member of the dojo in question. it was simply a situation brought up by a sensei and i was curious to see how other dojos handled it.