On Main Street, there's the aptly named Main Street Bake Shop, which does sell some breakfast items. However, I imagine that it would be <b>incredibly</b> busy in the morning! That's of course assuming it's open early for EE... common sense would make me think so, but I don't know personally if that's true. Grabbing something quick from the Poly is sure to be your best bet.
Personally, I never eat breakfast in any of the parks... it's so much easier to eat at the hotel, or have a breakfast bar before you leave the room, and then grab a snack later on in the morning. Since you're there early to make the most of your extra magic hour, I'd spend it actually doing rides, and not eating.