Charles Fox said that restorations were the most bloody of all revolutions; and he might have added that reformations are the best mode of preventing the necessity of either.
If you're working with a band and you really want to work them into the episode, you've got to say to them, "Look, we need you around every day and on Tuesday night all night because we need you to do voices as we're changing stuff. " We do the show so quickly, and you just can't get bands to do that. It's not really fair.