Assign emissive materials to the light group pass

I have an object with several materials assigned to it. Two of them are emissive. I'd like each emissive material to appear in a different light group. Currently this isn't possible, because only the object can be assigned to a light group.

I propose that the same light group option found in the object properties, is also made available in the material settings. This will also reduce a lot of work, because if many objects have the same emissive material, only the single material will need assigning to the light group, not each of the objects.