PP material access to poly normals but NOT material normals?

I want to apply a post process effect to certain objects (I’ll be doing this via stencils). The effect needs to use the object’s normals but NOT use the object’s material normals. Is there a way to do this?

So far the only thing I can find is a way for the PP material to access world normals. Unfortunately, that includes all the little details that ruin the effect. Since this is only a temporary effect, it’s not practical to change the object’s material on the fly.