I tried this one a few times the other day and it worked really well.
If you see a girl at the bar ordering a drink/ standing there waiting to get served go over and stand by her, soon as the bartender goes to serve her (we all know pretty girls get served quickly usually!) just tap her on the shoulder and ask her to get your drinks like your a part of the her group! heres how it went on one occasion for me the other day.
HB: (orders her drinks)
ME: (get her attention) and a double vodka and coke and a pint of fosters for my mate.
HB: haha, isnt it usually guys who buy girls drinks?
ME: yeah usually but you look like the sort of girl who likes to try new things.
the bartender then asked her for her money and she asked if i would pay! I said good try, smiled at her, and turned by back to her.
5-10 minutes later i saw and her friend sitting in a booth. I went over to them and told them id give them a chance for that drink they wanted... I did the 5 lie test on them and they failed, owed me a drink and i carried the conversation from there.