One of the advantages of orthographic mode is that the back/front silhouette is the same. Not true for perspective, however I do need to render two sides of an object in perspective such that the silhouettes are the same.
Ideally I would just invert the normals so that the backside would show, but this is not quite right due to internal volumes and such becoming visible. I think what I need is like the diagram below: when each camera ray hits the surface, it would travel parallel to the center ray to the other side of the object, then use the color of that surface instead of the hit surface.
Does anyone know how I could achieve this?
Adding an example render of Suzanne showing the problem of things not lining up due to perspective. I feel that ultimately its about what color is each pixel, so I want the back pixels' color to be used instead of front pixels.