Import visibility animation from a hierarchy only fbx

I think this is quite a normal workflow, I have an fbx containing a hierarchy and meshes and then several fbx with a matching hierarchy and animations, but no meshes.

The problem Im having is the animation fbx has keys on visibility but when its imported into unity those are lost.

Is there anything I can do to get them imported?

So far I've tried writing an AssetPostprocesor to add temporary MeshRenderers to the anim fbx in the hope that unity would make thr connection but no such luck