Duncan Di Saudelli wrote:

One approach could be to grind a flat on the top of each ball. Manufacture a
plane disk whose diameter matches the flat. A metal disk would enable you
to solder or braze or machine two pickup points at the edges of the disk,
diametrically opposite one another.

The suspender could be made from a strip of alloy, bent twice to make a thin
square U shape. The bottom of the U could be glued to the flat on the ball. At
the other end, a ball bearing glued to each outer face of the strip, or if
that's too complicated, a simple low-friction hinge. Alignment of the hinge
axis perpendicular to the plane of motion could be a trick.