I never did figure out how to do what I asked here, but I ended up using Mega-Fiers morphing and it works great. I highly recommend it to anyone looking for morphing ability in Unity.
I have tried converting similar scripts to use SkinnedMeshRenderer instead of MeshFilter / MeshRenderer… but have not had good success. This is primarily due to the fact that a skinned mesh in Unity is internally a shared mesh, and not a mesh instance. Due to that limitation, if you adjust vertex positions, you actually write those updated positions to the disk (to the data in your project).
If anyone else has information on that particular aspect of SkinnedMeshRenderer, please feel free to weigh in–,I have also tried to modify a morph script (a different one) that had a required MeshFilter component, and replace that with a required Skinned Mesh instead.