In this tutorial I show how you can create a sliding pivot foot roll using nodes. The first part of the rig is the same as Chris Lesage's rig and I only add some stuff on top of that to make it work for any shape.
EDIT: Here is the link to the ah_norCrv script. It is pretty basic and would need some refinement but it gets the job done. dropbox.com/s/swxdcn39bkltd58/ah_norCrv.py?dl=0
Make sure to visit Chris's site: chrislesage.com
And check out my blog for more: robotsquids.blogspot.com/