Relatively simple. Go start a new dynasty, create a coach, select a team. Go to the roster, edit all of the starters overalls to 99, or something around there. Once you've done that, save the Dynasty in two different slots to compensate for autosave. Then, sim the season. You can do that at your own pace, whether you want to save every few games, or what have you. Plan to go undefeated and win the bowl game. This should get you A+ prestige. I did this with Old Dominion after my first season there.