When I tried using a croll for a foot ascender last year, the main problem was that there was no way to keep the ascender from rotating around the foot when loaded. I solved that problem very simply this evening. This is the croll simply lashed to my right boot with a square knot.
With the angles involved, the rope fed much easier when the right foot. The success of the mission was thanks to the multidirectional nature of the croll's attachment point, which allowed me to do this:
The carabiner lay very nicely on the bottom of the foot, allowed me to comfortably tighten the lashing, and eliminated the rotation problems. Obviously, this won't work as well as a commercially produced foot ascender, but it is at least mildly interesting. I climbed the tree with it several times in a frog walker style, and it worked quite well once I learned the ideal dorsiflexion. Still need a tiny chest roller though.