I has same problem when try to push a texture to vertex shader (vshader - Cg) to setHeight for geoMipMap. I try many solution but nothing better.
I try to use glsl (with Ninth’s advise) by and it run.
[url]push texture to vshader sha file]
This my case
http://www.youtube.com/watch?v=7HTEZ_pX0bc