How can I set emissivity coefficient for each solid material?

In the steady-state thermal analysis considering radiation, How can I set emissivity coefficient for each solid material?
 

My model contains parts made with 5 or 6 materials.
Each parts of the same material has similar surface condition.
So, it is convenient if I can set emissivity coefficient for each solid material.

I know I can set the default emissivity coefficient at general settings of project but a uniform value for all parts is too inaccurate.
I know I can overwrite the default emissivity with desired value using "Insert Radiative Surface" menu. However, to pick and set faces individually is time-consuming task and I want to avoid it.

Flow Simulation