Just sparking some conversation here…
Do you think it would be possible to write a version of parallax mapping that would push up instead of down? I’m thinking that if you use a box as your surface with the bottom polygon as the plane, then the raised polygons of the sides and top of the box would allow you to render pixels at a height above the plane. I’m thinking aloud here and will need to sketch through the tracing math to see if the inverse of it would work.