I took another stab at this issue. I had to completely overhaul the way we compile Cg shaders, and needed some pretty obscene workarounds, but I think I fixed most of the issues. It should now be possible to use non-basic Cg shaders (via GLSL profiles) on AMD and Intel cards, as opposed to just NVIDIA cards, though subject to some limitations (with regards to which semantics can be used, for example).