From another site....
"hey guys,a good friend of mine found this.
right before the clock hits zero in the 4th quarter,hit the supersim option on the playcall selection screen.do not supersim,just back out.if you do it correctly,the clock will stay at zero and you can play till your hearts desire!!!!!
p.s this is only for the GS demo, XBL demo has no super sim option,happy playing fellas!
also if the game screen freezes,just press pause and resume game. if the cpu is down,they will throw deep EVERY play."