If you haven't done so already, call 407-824-5967. It is the phone number to the executive chef at Magic Kingdom. I took my son there who had multiple food allergies at the time (wheat, corn, soy, egg, milk, peanut and tree nut). We agreed on a huge bowl of oatmeal with apples (his favorite breakfast) melon salad, and bacon. They brought him all he wanted (he was only 2 at the time). You didn't say what the specific allergy was, but they are very accomodating. Good Luck and enjoy your breakfast.
I forgot to mention, that when we arrived at CRT the head chef came out to our table and went over with us which allergies he had and told us what was available and safe for him to eat. We found this to be the case at any of the sit down restaurants at DW, the chef will come to the table and make safe suggestions, ask what foods are your favorite, and try to make a safe version. They are very accomodating and knowledgeable. Good luck and enjoy your breakfast.