Mixing Sprites and Meshes with Nested Sorting Groups

How to make meshes and sprites behave in a shared sorting group?

I’ve dug a ton into how to render sprites and meshes coherently using the hidden renderer sorting layers option on meshes. I am so close to achieving the effect I want, but I hit a snag when trying to merge the meshes into the sprite sorting group.

Basically the system works fine without any sorting groups–in this image the outlines are drawn on quads and the character is made of sprites:

But as soon as I enable the sorting group on the character, the meshes no longer want to obey the sorting order and instead render on top:

I’ve tried messing with including nested sorting groups, z-axis (my game uses custom Y-axis sorting though), etc… kind of hit a wall. Anyone else had to solve this issue before?