This is going to sound a pain, but this is sounding like a sub forum type game.  Where each Mistress/sub needs their own thread.  So if Xany where to take a side thread, she would do it in "Mistress Club side story: Mistress Xany's pin cushion." or something to that effect.  Then anyone wanting to watch her could do so in her thread.  That would be just an example and we would each have one.