Start a new dynasty and choose a mediocre team. Schedule as many of the top ranked teams. Sim through to the end of the season and you should have a losing record and have less than 30% security. Play through the off season and you should be able to keep your job.
An alternate method is to start off by choosing Texas and become the head coach. Go to roster and edit everyone over 80 overall. Lower the first 5 options to 0 and then save. Continue that until all players over 80 overall change to 40 overall. Now go to your depth chart and make everyone that is now 40 overall a starting position. If you get to a position with no one that is 40 overall, just skip that position. It shouldn't matter if some positions have decent overall players. The positions that are most important to have starters at 40 overall are QB, HB, and WR. Now simulate to the start of the season. After that simulate to conference championship week. You most likely will be 0-12 at the end of the conference championship week. You will not qualify for any bowls, so just simulate to the end of the season. The achievement will unlock after the season ends.