I've tried this opener back in NY a lot of times and tried it this weekend when I went out with TheOtherI. I've said it in slightly different ways at times, but it has worked. I'm not a fan of being on the dance floor (loud ass music) but sometimes you just have to do it. There are factors that may prevent it from working though, such as when the target is with her group of friends and they "just want to dance with each other" or when it is a two-set, wherein you need the wing to handle her.
Me:(Walk up to her while she's dancing and get slightly behind her, body not facing her): I'm gonna dance with you now, but I don't want you to be all touchy and freaky with me ok. I'm watching you!
Her: (laughs and starts dancing with you)
From there, you can do the things you do(FTC, stories, negs).
I'm using the reason girls think guys wanna dance with them and using it against them. Hey, you're just there to "dance", not to feel her up and hit on her, right?

I think from the beginning, you gotta have the right body language to prevent her from thinking you want something from her. Let me know what you guys think about it and see if you can test it out.