That'd really be weird,
Dakęsîntrah, as the moviemakers of Hobbit want to closely tie Hobbit with LotR. That's about the point of casting Hugo Weaving as Elrond, Sir Ian McKellen as Gandalf, and Cate Blanchett as Galadriel. If LotR-Saruman would be Smaug in the Hobbit, that wouldn't do well for their agenda.
And I think Sir Lee was, well, unhappy with his scenes cut from the RotK movie, as discussed
here.
