Be charming, but don't steal the spotlight
This is not your time to shine. Master the art of being unobtrusively entertaining. Turn on the charm to capture the attention of the group, but once your boy enters the picture, fall back.
Levy just enough charisma to maintain the interest of the peripheral ladies (that's why you're there) but not enough to become the object of his desired woman's attention. Remember, you're not trying to win anyone over. You're only trying to warm up the scene, get the crowd ready for the main attraction. You're the opener, he's the headliner.