You're correct - ignoring the rest of the group would be socially retarded. So, just avoid doing that!
Compliment your target, and then share eye contact with the rest of the group to they don't feel left out.
For example
You (to friend): Hey, listen, I know this is a bit random, but I just saw your friend as I was walking past and (to target) I just had to come over and tell you, you look absolutely gorgeous. I'm _____ (to both target and friend)
HB: Thanks
You: So you two look pretty different for friends. I'm guessing you're the serious one, and you're the crazy one right? I bet she's all like "hey let's go do shots" and this one here's always like "noooo we have to be CAREFUL" and shit right?
HB: lol
You: seriously tho (to friend) is this one a bit mental or she she alright? Cuz I have this crazy stalker ex and I REALLY don't need a new one
Friend: LOL no she's really cool
You: Ok, great. (to target) Lemme guess - you're either an accountant or a brain surgeon
HB: lol, no I'm studying economics actually...
etc.
See - you talk to BOTH, and you can actually qualify, screen and neg the target "indirectly" through the friend, showing social intelligence by interacting with both and not leaving one out, and also showing you actually want to find out what she's like through the friend. Great to do for n-closing too "is that the right number?" to the friend is always good
