what I do is simple:
1) post-process the view and output the depth outlines
2) blur the previous stage only where there are outlines

For those who have normal stored in their G-Buffer, here is an idea on how you can get really high quality anti-aliasing with a image space post process, without using hardware anti-aliasing. First take the per pixel normal, project into screen space, and re-normalize. Then take this screen space normal, and rotate 90 degrees (compute the vector perpendicular to the screen space normal). This perpendicular vector will be in the direction of the strongest "edge" at the pixel. Now like screen space motion blur, sample from the screen in the direction of this perpendicular vector, and intellegently take a weighted average of a few screen samples along both the positive and negative directions on this vector. Would have to workout the details, but the concept should work really well.