Deferred Light Rendering: Prevent additional lighting passes on pixels in overlapping point lights

I have a lot of dynamic point lights in my scene (hence using deferred rendering), and often the point lights are quite close together. I am also using BlendOp Max, so often overlapping lights don't really change the intensity of light in those pixels.

I want to improve my performance by not bothering to calculate light on pixels that have already been calculated by a point light. I am wondering if anyone has any ideas on how I might go about changing the deferred shader to do this?