Shadow Catcher / Matte Shadow idea

Hi bros

I have an idea of the realization of a shadow catcher. It is inspired by Position Shadows for platformers. That’s how it looks now with Sphere Mask


The idea is next:
To show on the decal a silhouette of mesh and match it to the light source.
A possible solution could be to use the Camera, and clip from it our mesh with inversion (to left only mesh projection). And in the result gets a shadow shape like that:

Does anybody know the method of how to mask mesh this way?
Or maybe you know realization similar to the Marmoset Toolbag shadow catcher, which works with Built-in Light?