Maybe instead of going for a normal approach you can say something like "no way, I can't believe this, but you look exactly like my future girlfriend." in a joking exaggerated manner. It seems like it'd be a non-creepy way to approach a girl that could get a laugh out of her. A more laid back yet still comedic approach you could do if she's by herself or just with one friend is you could sit next to her and say something like "so what problems are you drinking away tonight?" They're both comedic icebreakers that could work assuming you say it right. I've never approached a girl before though so you may not want to take my advice haha, that's just what I would probably do personally though.