Did you know:
you can make your own stencil shadow code, since it is only projected on one plane at a time, not multiple surfaces, using models no less. Simply using an all black skin+ transparent/alpha, angle the model and squash it to the plane.
Somewhat difficult, but once achieved, a shader could easily soften it, and there would be no limit to the number of shadows you wanted from multiple light sources, or multiple surfaces.This idea came to me back when churning out garbage with A5 stadard, that did not support stencil shadows.