A girl I met off of Facebook in college used this on me and I've always had great luck with it.

Girls are a bit weirded out by the online dating thing, so you have to pretend you are a little bit too. Tell the girl that you both will have to come up with a something to tell other people how you met.

I use the line "I agree, online dating is a bit weird still. We'll have to think of an awesome way we met. Maybe...Scuba Diving at the Great Barrier Reef, or you were Skiing in the Alps and gave me hot chocolate (thanks again), or *insert something that she likes to do...and then make it adventurous* dancing tango in Argentina and we were the only Americans in the city. What do you think...?"

I would alter it to fit her profile, but as a second line it works great, as an opener it holds its own. I think the key thing with any opener/routine is just to show her that you're creative, you're fun and you're DIFFERENT.

Best of luck guys.