Well there's source code included with that shader. Time to start learning MR shader code it sounds like :P. Either that or find an interested programmer.
What shader are you using and what are you rendering with? If you could post an example screenshot of the type of shader you have and a photoshopped comparison showing what you want to achieve that would help to understand what you're trying to do. It seems like an unusual thing to want to do adjusting the gamma on a…