This is not about the T & S whitby, singarounds, singarounds are difficult to manage, I've done it, and sometimes I have sounded like Mrs Doyle, "Go on, go on, go on" when asking for a known performer to join in, now , if the don't ask they don't get asked, it doesn't have to be formal it can be as discreet as a sheep auction, look into Graham Metcalf's eyes and if you get a response of a slight turn of the head to the right accompanied by a lowering of the jaw then you get a song, if he stares straight back you won't.