How to bake emissive objects into lightmap?

I want to create a City Night environment with some lit windows on the buildings. I want those windows to get lit by the lightmap.
When I use emissive shaders with the window mask as illumin map, the windows illuminate other objects, but don’t get lit themselves.
To show this, I did a simple test with a emissive ball and a plane.

What I got was this:


Only the plane gets the lighting from the bal.
Nothing gets baked in the balls lightmap.

What I want to achieve is this:


I can’t use emissive shaders in runtime due to performance reasons in mobile. I must use unlit(supports lightmap) shader. I need the sphere to get lit by the lightmap as shown above.

Is there a way to do this??


The usual trick is to paint the windows to be bright white in the diffuse texture. That matches the emissive behavior in the rendering even when you use a simple unlit shader in the real game. Basically, paint the building night texture as if it was a photo of the building at night.