Unfortunately pretty much every domestic first class fare is an instant upgrade fare nowadays. Assuming we are talking about regular two class aircraft, then the only way to avoid this is to buy a J class fare (F class fares don't exist on these flights anymore) but these are usually around five times more expensive than the lowest advertised first class fare. These instant upgrade fares are based on a fixed upgrade amount from the relevant economy fare, so I'm pretty sure you would get that element refunded if you asked.