You can totally upgrade cute girls in the gate area. If your friend really wanted to give her the full service, he should have taken her to the PC and done the upgrade while she was having a drink.

If you want to be really chivalrous and not take advantage of the true intentions of the system, just sit next to her in coach and trade your FC boarding pass for that seat when the ticketed passenger shows up.

Even when I'm traveling with someone on the same route, I book on a separate itinerary so that I'm eligible for EUA at the plat window.