I've actually seen this one work before...

There were 2 or 3 guys standing around talking, drinking etc. I don't know them but anyways... this was the line one of them used:

The really pretty girl walks past, and one of them said loudly, so that she could here, "omg guys, i think i just saw my future ex wife". She stopped, laughed, and started conversation. I think what makes it easier is that you're saying it to your friends, and not the girl, haha.