Everyone knows what they're bringing to the big meal. And family members would protest if Mom didn't make her cranberry salad and if sister changed the dressing recipe. Some things you just aren't allowed to mess around with on Thanksgiving except maybe
Once they've filled their stomachs with excessive amounts of tryptophan causing them to reach a vegetative, comatose state the final course could be changed up a bit and they likely would never see it coming. That's because it's a little like some of them feel as they gaze at the football game on television: fluffy, yet slightly dense - Pumpkin Brulee.
Make it the night before then torch it just before you serve it. (If you don't have a kitchen torch, the broiler will do.)
Near the end of the first half of the football game, offer them an ever so small slice. Chances are those slouches on the couches will be on their feet scouring the house for more during half-time!