I totally believe in this. I think actually there are studies that show, e.g., that moving your facial muscles into a smile improves your mood!
As they say in some 12-step groups, "fake it until you make it."
I agree that "fake until you make it" is a good strategy for creating change. But it only works if we fake it because we recognize there is something about ourselves we want to change. The Doc was faking it to please Louisa, he wasn't faking it to affect a change in himself. In my opinion, it is really for the wrong reason. I agree with Louisa, you do have to want it in order for it to work.