I haven't tried the custom solution from Egert above, but I did implement the coordinate system set up that Tomek suggested. It works pretty well, but I'm wondering if anyone know why it doesn't show up in the viewport. It works perfectly once you start karma, but the viewport shows a weird tiled version of the texture. It doesn't make for the most artist-friendly set up. I looked into all the material bindings and don't see why the ndc coordinate system wouldn't be picked up by the viewport. Any help appreciated.

Ah, it looks like the coordinate system approach is karma specific. Someone let me know if I'm wrong.