Handling multiple lightmaps in a scene

I have a scene with 4 different light sources:

• Daylight

• Moonlight

• Interior Light

• Some interior items light (like a tv on)

And I want to blend them depending on which ones are currently active, the Player can turn on the TV or the Interior Lights, and the day/night cycle is handled by the game.

I want the lights to be baked so I can have nicer shadows and avoid any calculation on the player side.

I managed to make 2 lightmaps be switched depending on player input. But when it comes to more than one. It can be a litte tricky.

I know I can bake the scene in all possible arranges of light (DayLight + Interior + objects, Moonlight + No Interior + objects, and so on), but this would be a waste of resources, and in large scene impracticable, where there's many interior lights and objects, the amount of lightmaps needed grows exponentially.

What's the proper way to deal with multiple baked lightsources?

Is there a way I can create a lightmap on the fly by merging 3 or 4 other lightmaps? In this case I would only bake each different light source, then depending on the player selection, merge a new lightmap with all the sources in one.