Material ID Pass with Knockout?

[Evox_Productions]

Is there anyway to render a material ID pass with a knockout of a texture. For example I am rendering a car. The paint is a blend material. Within this blend mtl there is a shader that has a transparency map, so the carpaint can can have decals on top of it. Now I want to render a matte pass for the paint that has the decals knocked out of it. I know I can do this in a render layer, but Id really like to know how to do it with just a render element.

[tinuz]

I think one way would be to put the transparency map into an extraTex element

[Evox_Productions]

Wont that effect all the Geometry? I only want the decal on certain objects.

[Evox_Productions]

I got it to work by creating a material ID pass and then pluging the outcolor of a surface shader,which containins the matte, into the vrayColorId of the surface shader's shading group.