Mendelmax y-axis 180 degree bearing retrofit

In case you haven't heard, the mendelmax 1.5 y-axis suffers severely from being overconstrained; for an excellent explanation of what this means and how to fix it in general, see bilsef's post here: http://goo.gl/U2XJN

The gist of it is that one of the rods needs to be constrained only vertically, by a setup alternatively called an idler, follower, or 180 degree bearing. Using cartridge roller bearings for this is slightly less than ideal since they're not designed to take a point load (effec