Copying objects with lightmaps intact

I'm making a small visualization for the web, which involves a mirrored floor. I've flipped around the scene to get a mirrored image on the ground and it looks good. I'm having trouble copying the lightmap though. They don't seem to be duplicated. Is there any workaround for this?

It's not really a straightforward process, but it is possible to achieve this via Renderer API. Take a look at the lightmapIndex and lightmapScaleOffset properties.