Whenever a team backs out on a contract with another team, give the team that backed out a +2 in the BCS and the team that was back out on a -1 or a -2. (Remember that lower scores are better) That would make the VT's of the world think twice about backing out.
I'm 100% in favor. Anoter possibility--if you back out, your SOS is based on your opponent's replacement rather than your own, if your opponent's replacement is worse.
If you had this there would need to be a time table. Like after Jan 1 you can't cancel a game you have for that fall.