I discoverd a little trick to use normal materials as stencil map instead of the geometry node. With geometry nodes one cannot use cube, tube or sphere mapping. One has to use uv mapping.
The trick is to use an emit value of 1 in the shader setting of the alpha material.
Press F12, then change the emit value to 1 (Shader of the Alpha material) and render again. This method is handy for planet materials.
Thank you for the example file, I will try it out at lunch 
I tried to download it yesterday, but the dial up connection at home kept bouncing me offline
Another alternative is to set the Shadeless Button [Material Panel]
Example picture with three materials. Orange, blue and black/white texture as stencil material. Picture left hand with emit=0, right hand emit=1
