Do exactly as DeltaMIA said. Otheerwise, your boarding cards will not show you as a Silver Medallion when you preboard. And like everyone else said, go ahead and call. If you are not cleared by the time you reach the airport, tell the agent that you want to be placed on the upgrade list, or if checking in at the kiosk, just press the upgrade link. After you go through the upgrade process on the kiosk, it will then continue to check you in. When you arrive at the gate, just watch the upgrade list on the GIDS until you see your name clear. However, if you are number one on the list and there is a chance to clear, but you board, you will lose your spot on the list and it will go to the next person waiting for an upgrade.
I don't have a microwave, but I do have a clock that occasionally cooks shit.