Normalizing linear gradient masks

Hi All, I'd like to know if there is a way to use the normalize tool on a layer.

I have a series of fine art reproduction images, paintings hung on a white wall, with a natural difference in illumination (brighter at the top of the frame than at the bottom) which I would like to even up. I have been adjusting the exposure difference using the linear grad tool but thought it would be good if I could pick an area with the normalise tool and then apply it a graduated mask. The object would be to have an even exposure and white balance across the frame. 

Has anyone been using the tools in this way? I can't seem to get a result but feel in might be possible.

ian