Inverted Depth Map (Draw farthest geometry over closest)

I require a inverted depth sorting, best inside the material shader. As mentioned, the farthest object overdraws the objects nearer to the camera. Yep, looks strange, but that's how I need it.

So far I tried Cull Front, ZWrite ON and ZTest Greater, but t$$anonymous$$s approach requires a model in front of the camera, otherwise I don't see the result.

Maybe draw two triangles inside a Posteffect Shader? Hope anyone can help me.