Projective Texture problem:REVERSE PROJECTION

I have realized the Projective Texture Mapping to simulate the Spot Light.I have a problem:THE REVERS PROJECTION.What is the correct way to elimiante this problem???

I did it by placing a user clip plane at the near plane of the frustum for the projector. This culls the geometry behind te near plane, i.e. closer to the light.

Can’t it be eliminated via the vertex programs?
I’ve not used them yet but I think it’s possible to transform the texture coord from there and then make a simple conditional test to eliminate the unwanted part (I remember you can’t directly do conditional instructions but NVIDIA has some example on how to do pseudo-conditional instructions)