This is a tough one isn't it, I've looked into it myself.
I'd suggest that instead of looking to open girls who are already dancing with their friends, try opening sets at the quiet bar. If there is no quiet place in the club, often there are shelters outside and/or smoking areas, these are also good places to open.
If there is a real HB10 that is on the dancefloor that you really want to pull, make sure you come across as fun and interesting. They came out with their friends for a good time, and you don't want to be cramping their style and putting a dampener on things. But also remember that, by going out, they probably want to meet new people. Anyway, it can be difficult to seem fun and interesting without and conversation. What I sometimes do is dance near a set, without engaging them at first. Make sure you're in a group when approaching on the dancefloor (mixed with guys and girls would be best - social status), as people who go to clubs on their own can be seen as weird. I then start doing some funny moves, having a good time with my friends, and smiling - a lot! This will make them want to be part of the fun you're having. I would then include them firstly with some eye contact, then some fun moves (nothing too touchy at first) such as a twirl, etc. Gradually, as she gets more comfortable with you touching her, become more intimate, and head in for the k-close
Hope this helps, sorry if it's a bit too long-winded!
~Deebo