well as you know, the whole point is to make it seem like you're not hitting on the HB.

Don't talk directly to the HB when in a group, unless it's a neg, or at least very quickly.

Try and stay with the group for at least 5 minutes. It seems like an age in reality.

Once you have gained social acceptance from the group, ask them whether you can
borrow the target/show her something/ask something, "over there". Point to the place as you say this.

A great way of increasing the probabilities of her coming is by locking her in with a prop. Put a hat on her head and walk off, this way, she HAS to follow to give it back to you!
Then, once you've isolated the target, game on.
Try and think of 5 ways of asking the group whether you can borrow the girl, post them on this thread when you're done, would be good to see your ideas.
Hope this helps.