Integrated Cupcake Z-Rod

This is a spin-off of the Wobble Arrester by twotimes:
http://www.thingiverse.com/thing:2151
I love his idea, but I had a hard time getting the offset linear guides to work properly - my prints always had a sort of blobby section right at the top, which took my bushings out of alignment and caused binding. No doubt I still need to work on my skeinforge skills.

Anyway, I figured that ideally the Z-rods should be somewhere in the middle of the Z-stage - in other words, between the drive screws. This should reduce binding and in the event of a crash won't load the Z-rods and bushing clamps as badly. It also turns out that there's space enough to add the standard makerbot rod mounting scheme: through holes with external covers, although the covers are a little different due to space constraints. I have uploaded DXFs that can be used as templates for modifying your top, middle, and Z-stage; if you have access to a lasercutter you could use them to cut drop-in replacements to the st