simulating 3D planes with 2D physics engine

[urbien]

2D Games have been using parallax effect to create a depth of field feeling. Web sites recently started to use this technique. Some mobile apps do that too. See for example Pandora using content as a layer that is closer revealing menu in a background that is moving as well (note menu text changing its distance to the edge):

There seems to be a simple way to create parallax with css (and it works fast as actual transformations are performed by the GPU):

1. give depth to brick on Z axis, e.g.:
   translateZ: -30px
2. set perspective on a container:
   -webkit-perspective: 500; -webkit-perspective-origin: 0 0;
3. change perspective origin on a container as we scroll/transition:
   container.style.webkitPerspectiveOrigin = scrollXdelta + "px " + scrollYdelta + "px";

So, how does one utilize physics engine to help with this, or do we need to do it outside of it?