I'm just wondering if it's possible to render self-shadows (shadows cast by an object onto itself) as a pass. It seems the only shadow pass that can be rendered is received shadows.

While the colour and diffuse pass both contain self shadow information, my cast shadow pass looks terrible when composited over top of the colour pass. Parts of the cast shadow are missing where they would be starting to blend into the self-shadow.

What i want to do is render the entire set of shadows for each object (received shadows + self shadows for my subject, another set for my background, etc.) Effectivly, this would render my object and background as their material colour without shading and then apply the shading in the shadow pass.

This would give me way more control over my shadows in post.