In deference to different genders and orientations on the forum, I'm still searching for the right way to put this, "hot young passsenger" is stilted, and who am I to put down experience?

In any case, if you see the empty seats coming, from checking seat maps or whatever, the thing to do is to pick a passenger whose company you'd enjoy, and try to get them a companion upgrade. There are ways to word this that don't sound like a pickup, particularly if it isn't the conversation opener.