This may be a derivative of Jetguys http://www.thingiverse.com/thing:6184, not sure, but it was definitely inspired by it.
I don't really like bushings so I will slowly be moving to bearings where ever I can. I liked Jetguys idea and it makes good mechanical sense. But one I didn't really want to modify my ToM permanently with the tubes and I would have to pull it apart more to do that. Two I wanted to get bearings on the Z axis. My first thought was to use a linear bearing and it still may go that way. But this seems to be working from my preliminary tests. I haven't done any hi speed tests or anything of the sort. Just a basic cube.
This may be a WIP not sure :) we'll have to see how this one works out and see if there are any improvements. If any one else builds this I would really like to know your results. This was designed for the HBP it won't fit with the ABP.
Print one then mirror on X axis and print another. Attach 2 3x8x3 mm bearings to the two mount points on the bottom of each support. Remove a Z axis rod from the top, remove the lower bushing. Remove the 3 screws holding the bottom plate and using longer bolts, I used 20mm cause I had them laying around. Attach the bracket to the bottom plate. The corner bolt is a bit tricky to install but it goes easy enough. Make sure you use a ball hex wrench though. Replace Z rod and repeat on opposite side. Recalibrate your Z height, as it may have changed the angle of the Z table. Oh I forgot I made the mounting holes a bit small because right now my printer has a problem with printing the holes. So you will have to drill the 3 out. The holes where the bearings mount are intended to be tight so you can thread a bolt into them securely, don't drill those out.