The best ways are as noted in the other thread. Day game after a night game is a good indication.
However, if you're looking for a way, the lineup cards are usually posted on yahoo an hour to a half an hour before game time. Since you can make cahnges up to five minutes before the games starts, if you click on box score and he's not in the lineup, replace him with your backup. Tough to always be at the computer that close to game time but if you can be there, that should work.