Hi,
It’s actually this tool
Surface Follow from 2016 Blender Conference - Coding / Released Scripts and Themes - Blender Artists Community
It’s free
But yes, basically the point is to flatten the mesh to UV in 3D space and then binding new mesh on top of it, then using blendshapes turn the flattened mesh back to original shape and cleanup.
EDIT: wow I just realized the plugin is from Rich Colburn. Didn’t know he made a plugin out of it. Thanks for letting me know 