@RyanB - You probably right about the line sphere intersection… though my coordinates are definitely reaching infinity at the edges away from the Light vector. I think I have it working for the front (GB) coordinates. This seems to work for that section regardless of the light vector direction and the objects orientation, so that’s fine. The key was to also multiply the offset UV’s against the Dot of the light vector and surface normal, which prevented it going crazy near the edges and tiling way too much.
The problem i’m having now seems to be the swizzling to make it work with RG (top/bottom) and RB (left / right) , which seems to be skewing the UV’s as well as pushing them back, so I’m unsure how to counteract that. This is looking at the sphere from the bottom up, with the light vector being 1, 0, 0. This also doesn’t work for anything other than a 1,0,0 light vector.
Somewhat annoyingly, the shadows on the top move toward the light vector, whereas underneath they move away. That part should be hard to fix though.