It all depends on the airline. UA has a system in place where others can make their own reservations (or I could, for example, my dad make a reservation for me if needed). I wouldn't be surprised if US had that as well, they did have a pretty nice system as I recall from my SkyWest days. But to be honest, I would be really surprised if AA did have that option. Odds are, the employee will have to make your listings. DL works that way as well.