This all started with the need to have a foot roll. So instead of using the standard 2 corner nulls I have a dynamic pivot :) Here are some implementation how to get the pivot position.
Left: Finds the closest vertex on the mesh floor vertices.
Middle: Finds the closest location to a curve matching the disk edges.
Right: Just takes the controller XY values to conform over spherical coordinates by applying the Arc Lenght forumla to find the angle.