Thanks Matt, I don't want to just stick the lights in the cake. I want to do it in a way that the front part where the eyes and mouth is , to be hollowed but I don't know how to go about that and how to support the cake in the front.
In theory I suppose you could hollow out a chiled cake, on the inside, but just enough to insert one of those plastic christmas ornaments, that you can get to fill and decorate in craft shops. Usually you can get those in different sizes, plop LEDs in that and insert into cake. When you then out the second cake on that, the ornament should be stable enough to hold up the cake, sort of like an inside (round) dowel and you won't have to worry about the cake collapsing on itself
One of my friends did a pumpkin cake that had a cake in the back half and the front made out of gumpaste. The front was basically a shell, if I remember correctly, so she could put lights inside and it looked like a real carved-out pumpkin. Best pumpkin cake I've ever seen http://www.welldressedcakes.com/index2.php?v=v1 It's in the carved cake gallery