O.k. when I leave a set this is what I do. I'll introduce a time constraint at the start and when we are building a good rapport I say I have to go and I turn as if to leave, take a few steps and then I looked round to them and said "What are you doing still there? Come on we're leaving this shit hole" The first few times I said it, I got an awkward look and a few came with me out of "pity", I realised this was because I said it without confidence or conviction. If I want them to come, I have to let them know I am going and don't really care if they come or not, now it works every time, take them somewhere to eat and speak. Much nicer than in a noisy club I think.