You've already got the official answer.

I had a few times, where I've booked for my family with my wife's name given as an additional guest. Wife and kids checked in first, I've arrived very late. I wasn't asked to show up at the check-in in person and we've got all benefits.

But - of course - that is not the same as booking for a friend and his girlfriend.

If you book a room for three, do the check in person, but don't sleep there, it shouldn't be a problem, even your head never touched the bed.