Hi, a few weeks ago I invented a little neg I used couple of times since with pretty good success in getting the girl to qualify and shift the SMV battle your way.

It's common knowledge that you should leave the convo in the upbeat so next time, when you are in a bar and you are doing great, just say:

"Hey, I'm gonna go get myself a drink. You want something?" - then give her a puzzling look like you are trying to figure her out but before she can respond, jump in with "Coke Zero, right?" with a satisfied smile like you figured it out. In the same moment, just turn around on the spot and walk away to the bar.

Give her no answer to question why did you think she would like sugar-free drink (obviously implying weight) and let the hamster spin. If she confronts you with it when you return with the drinks, just say "No reason."