Well, I was there a couple of years ago and they had two floor singers who came on before the main act. I'm not sure if they were professionals or not (come to think of it I think one was, not sure about the other). But it wouldn't hurt to give Paddy Ehbort a call or drop him an e-mail (I think they have a website but am at work and can't research it - try a google)explaining your situation - and maybe make a simple demo to send out. If you're only doing one or two songs it wouldn't matter how big your repertoire was, as long as you sang those couple of songs well.