First off this takes a wingman who either has a girlfriend or is okay with not getting laid for his efforts. Basically a good friend.
Have the wingman approach girls with a rejection-proof opening. "Hey, this is going to sound weird, but... I'm trying to get something for my girlfriend for her birthday and I need a female opinion."
The wingman is automatically disqualifying himself as a potential suitor, presenting himself as a trojan horse.
After he talks with them for a few minutes about it, I pop in from across the bar and interject. The girls' sexual defenses are down so this leaves them open. My intentions are still concealed as well as I am just following a friend who veered off to get a female opinion.
This worked wonders for me. We gamed a 2-set of HB8s for over an hour, I got one's number but the bar closed before we could escalate anything. Still, I expect good things out of it.