(Clay Render) vray lighting workflow?

I have prepared archviz interior scene with all the materials applied. i want to test lighting. i want to apply clay material ( like vray global material) to all objects just to test the lighting with fewer objects so that it takes less time to compute. after testing light disable global material and compute high resolution lighting with all the materials. i am not talking about 'lighting only ’ mode in viewport inside ue4 editor. I
s this possible ? I guess ,This method is also useful in producing uniform white light in whole scene without getting color bleeding in GI. How to do this? any help?

no one?