You can check goaliepost.com or leftwinglock.com or even hockeyinformer.com if you don't mind pop-ups.
If you are available before the start of the game, check the "box score". Sometimes Yahoo will reveal the actual starting goalie anywhere up to 15 minutes before the slated start time. But not always. Usually about 3 minutes before if at all. Then you can quickly make your changes.
This goes for forwards as well, but you get WAY MORE advanced time with them.