I can adjust the near clipping plane in the frustum culling to avoid the problem, but I also ran into the interpolation problems mentioned on cameni's blog, so I went back to the split scene solution for the time being.

However, I was wondering if this could be done per fragment instead of per vertex? Wouldn't this eliminate the interpolation problem?

@cameni: The problem was that all objects close to the camera were culled by the near clipping plane in the software frustum, indicating that the z coordinate before projection was closer to the screen than the modified depth coordinate in GL.

Great, thanks! I'll check it out