Different reflection cubemaps for different materials?

Hi,

I need to use two different reflection cubemaps for different materials. If I'd write my own shader would it be possible to assign a specific cubemap to use for reflections?

I am making a WebGL archviz thing with more than 40 houses, the windows and facade need to reflect the skybox and some reflective materials inside need to reflect a cubemap of the inside. I tried using reflection probes but it wouldn't bake, I guess 40+ reflection probes isn't ideal. It doesn't need to be perfect, as long as I can assign different cubemaps for reflections. I tried finding information about adding a reflection cubemap in a custom shader but didn't find anything yet, please point me if that direction if you know any tutorials or references.