I tried some things out, and came up with this :
https://www.desmos.com/calculator/lhieagxzdy . What I'm looking to do, is find a way to use an entire equation as a whole as a projection equation. There should be a way, either with matrices, or something else, that can do this. The current consensus on perspective projection rendering seems to be for single points at a time. I can't find anything on a whole set of points at once that can be used in a similar fashion.
The function:
(x - a*sin(t*\pi))^2 + (y - d + f*cos(t*\pi))^2 = (b - c*cos(t*\pi))^2
a = translate dist from origin along x
b = radius of sphere
0 < c 1 : scale coefficient for near/far sphere shadow , 0 = orthographic , 1 = infinite dist , 0.3 is good
d = translate dist from orig along y
f = upper/lower limit of y-dist from orig of sphere center, simulates oblique angle
0 < t < 2 : rotation of sphere shadow
It's still not exactly what I want. It does emulate the xy projection of a sphere rotating on the xz plane. But, the function that emulates the oblique angle by rotating on the yz plane doesn't correlate well with the scaled radius size of the circle shadow (as it should!)