mainly what we've seen is some (not all) of the venues will add holiday items to their regular menu. like at the buffets you often see something "holiday" added. sometimes it's what we think of as traditional items, sometimes it's just a dessert added to the menu. we typically go right after thanksgiving and for instance california grill had a dessert with peppermint, chocolate, and egg nog ice cream they'd added to their menu. if you can whittle it down to which venues add thanksgiving items every year you can be fairly safe they will again this year. if you have a specific venue in mind you can always call them directly.
if you want to have a little fun think about doing something totally nontraditional...give everybody a vote as to where to eat or what kind of food to eat instead of traditional turkey etc... after all you're on vacation and being nontraditional by being in the world anyway. we did christmas dinner once at flying fish, once at coral reef and christmas eve once at 1900 park fare.
we stayed in a suite one year that had a stove and my mom (who decided to come up for the day only) brought "thanksgiving" with her and cooked it right there in the kitchen in the room. she had prepped everything at home the day before (we only live 2.5hrs north of wdw). that was our most decadent thanksgiving ever lol.