I don't know of any places at MK to do that...I do recall seeing one at Universal a fews years ago. There are several photo spots makred on the maps as pointed out by safetymom. Those spots are also marked with a Kodak sign at the actual location. I believe the one for the Castle is to the left as you face the castle - in fact, I believe there is one to the left and the right of the castle on the walkways to Adventureland and Tomorrowland respectively.
On a side note, there is a great scene at Downtown Disney with four or five characters scupted from "snow" - I got great shots of DSs there in June. It's behind the Christmas store - on the parking lot side....