Erikstormtrooper said:
A lightsaber is the same from all sides. A face is not. To replace a face as it turns, you need the replacement face from all the same angles. Plus, as humans we are trained to see faces; this would have to be seamless for it to work.

hmmm....I guess using all the video clips available from ESB, combined with the ability to slow down and speed up the footage, as well as morph and tweak the perspective, would provide enough. It would have to be approached on a scene by scene basis. It doesn't help that the puppet Yoda in ROTJ looks off too. I think the CG Yoda was modeled more after that one, looks more like a chipmunk...