You would like that :

and you have thit :
or thit
.
No problem, I've the solution.
For begin, we set the material : set Alpha on zero and push Z-Transp (or Ray-Transp).
We use four textures.
- The first is for opaque color (here the black). You can delete this texture and the opaque part will have the color of your object.
- The second texture only in Stencil
big picture
- The third for the transparent part's color.
big picture
- The fourth on Alpha
big picture
The end, normaly it's ok. Note : i've a white picture with black logo. It's important for alpha and stencil. If you have a black picture with a white logo you will set oposite.