The original thing 44572 wouldn't work for me because my teflon block was too wide. I reproduced the same idea with openscad so I could adjust all the dimensions and added a nut trap while I was at it.
This does a great job preventing the head from rocking and messing up the print when it moves near the back of the print bed and the wiring harness and/or filament start making the head move.
After printing, I used a 1/8" drill on the holes so M3 bolts fit easily. I ran my spring from the hole in the end of the arm to the top corner of the fan. It isn't applying very much force, so the head can still rock if it has too, but normal movement of the carriage no longer makes it rock.
Additional pictures and babbling about this (including examples of how it improved my print quality) can be found at http://tomhorsley.com/hardware/solidoodle/solidoodle-springload.html