Remix from http://www.thingiverse.com/thing:724999 and http://www.thingiverse.com/thing:1128468
While cutting a large print I had one of the belt tension zipties come lose and cause the endmill to drag an 1/8inch too low across my carving, so I looked around for a different way to keep them tight. Most of the other tension devices require you to reprint the corners, so I modified one version to fit the original corner.
Part A requires you to replace the whole top side of the corner, but Part B slips into the original Ziptie hole of the lower corner. You may have to trim the tab on Part B to fit into the original Ziptie hole, but I figured it's easier to trim off plastic than add plastic after the fact.
If you decide to use the loop bolts like I did, take note of which side of the printer has the most room when the slide goes all the way to the end (most likely the tool side). I didn't and I lost a little bit of room on the non-tool side because the slide now runs into the bolt. This is easily fixed if you put the bolt on the side with the tool. If you don't want to use loop bolts like I did, then just print 2.stl from here: http://www.thingiverse.com/thing:1128468
If you need to flip the parts, just use the mirror function in either Cura or Repetier host.
Lastly, if you compare the photos to the STLs, they're a little different. I modified both Part A1 and Part A2 to bring the belt a little closer to the bar. I noticed when I printed the original versions they stuck out a little too far, but it doesn't really hurt anything and I don't want to waste more plastic to fix it for myself.