Using SpriteAtlas as texture in custom shader

If I have a pre-made texture atlas for a 2D game, I can use the editor to slice it in grids of quads and use the resulting texture in a custom shader, where I can apply also other textures of the same sprite-sheet (normal maps, subsurface scattering etc.)

The problem of course results in having quads instead of polygonal meshes surrounding my sprites, which adds potential overdraw to the application and reduces the number of sprites I can pack in a single 2048x2048 texture

The new SpriteAtlas system creates an atlas from a set of sprites, which are delimited by polygon meshes instead of a quad, but unfortunately I can't use the spriteAtlas as a texture for a custom shader

How are you supposed to use them in this scenario?

 

You need to extend and create your own solution for this I believe.