Export FBX with just bones and blend shapes?

I’m able to animate a SkinnedMesh by importing separate FBX files containing only skeletal animation data and it’s cutting down on my files sizes a lot. I’ve tried to expand upon this concept to include blend shapes but I’m running into a snag with my FBX exporter. I’d like to just export the joint hierarchy and the blend shapes then apply those to the SkinnedMesh, but it looks like I need to have geometry selected during export in order to actually export the blend shape data.

So my questions are:

  1. Do blend shapes require a mesh to accompany them during export?
  2. If it’s just a requirement of my exporter, could I somehow create a custom exporter that ignores mesh data and just publishes the joint and blend shape data?