This is a really simple modification to Techson's design found here:
http://www.thingiverse.com/thing:575489/#comments

The original STLs were in bad shape, mine just fell off (loose/unconstrained nut trap), and the top "clip" geometry had an overhang that wasn't very conducive to printing.

I just remade the file (no errors), added a chamfer to the overhang, and added a small layer between the bottom of the bed and the nut, so it holds tight to the bottom of the Y carriage.

Enjoy!

P.S. Warning! The Gcode attached is for the 12" Makerfarm i3v, so it may not fit your buildplate! Sliced in Simplify3D, so it's nice and clean :)