It's hard to explain what I need to achieve here, so please feel free to change the title and text.
Matcaps are a real life saver when I need something rendered fast, but there's one issue I'm unable to solve. Suppose I have a statue with a golden matcap material on it and I want to animate its shine as if the things which are reflected on it are moving, or it is moving itself but the camera is attached to it. With matcaps the only way to do that is to change the orientation of the camera relative to the model with the matcap on it. Here's what I want to achieve:
Notice both the model and camera are static.
I've made this possible by applying a "Normal Edit" modifier like so:
But this doesn't look quite right as the results are mixed as seen in the modifier settings, not overwritten.