Trying to figure out how Roblox converts Shirt templates

I’m making a tool that allows you to live-preview 2D clothing as you create it by mapping it to an R15 rig, however, there’s certain blending steps between the shirt and the mesh texture ID, that I’m not sure what it’s doing. To save some time, this will only map to the block rig (as I can imagine Rthro and other block rigs could do even wackier stuff).

For a technical explanation, when exporting a rig as a mesh, you get this texture map:

You can extrapolate each of the UV maps by coloring different parts of the rig, which gives you this:

.

I can cut up each part of this UV texture and apply it to each mesh part easily with an EditableImage, but again, how do I generate the blending parts for the bevels, and hidden parts (bottom of the upper limbs, for example).

(Only for R15, R6 has some REALLY wacky UV export).

or, y’know, roblox could support EditableImage on more texture instances…