Is it possible to have lightmapping on runtime generated combine children in Unity? It is possible to bake combined meshes when they are done in the editor, but the .apk/.ipa size increases too much.
You could use LightProbes.
Light Probes Group from the editor. When you bake the lightmap it will be populated with info on the various light sources.
If your combined model
MeshRenderer are receving probes (check
Use Light Probes in the inspector), then the shader can calculate approximated lighting coefficients sampling them from the probes structure at run time.