Bash him over the head. We all have to play songs we wouldn't necessarily listen to in order to entertain, it's the job, innit? It's not about him, it's not about what he likes, it's about the punters. Give the punters what they want, simples. He needs to get that through his thick skull, otherwise every time I've played "Don't Stop Believin'" through gritted teeth has been for naught.
People have been sacked from bands because of this stick-in-the-mud attitude before, and just because he's BL simply means he could end up bandless.