First and foremost, not every girl has the capacity to be aggressive. Many girls that are aggressive are the kind you probably wouldn't want to have sex with. Lastly, I know some of these dudes lie. If you're making it with these girls, you're doing something right, so don't worry about these stories you hear.
This isn't my strongest area, but I've had a few experiences where I was not the aggressor. Each time, the perception was that I was a hot commodity, and that if the girl didn't act fast, I would be gone. This was communicated through body language, negs, IODs, and all that other PUA jargon.
Try talking to your target for a few minutes. Suggest interest, but don't confirm it. Then, talk to an equally hot (but slightly less desirable) girl near her. Repeat. Come back to your target eventually. If she has some nosy friends, disarm them. Stick around with your girl a bit longer now and build a lot of attraction. If she's got aggressive genes, the thought of you going and getting snatched by another girl may make her a little more sexually aggressive (alcohol probably helps too
). Act like you've got somewhere to go, but don't say it. She will sense it if it's communicated right. I realize everything I just said depends entirely on the girl being aggressive. That's probably the truth about it. Aggressive girls will get aggressive if you give them a reason to be.