Edit :31-07-2018 remove the compatibility to MK2.5 due to endstop. Check vekoj design for new versions.
Remix to add clamp to vekoj(https://www.thingiverse.com/vekoj/about) idler design. All the informations shall be read on his thing, you will need the tensioner from his files (https://www.thingiverse.com/thing:2846079).
It will ease the insertion of bushing and then secure it firmly.
Be carefull, this design will work with zaribo style extruder as it use a 16T pulley instead of 20T on stock.
Additionnal BOM :
4 x M3 nuts
4 x M3x10mm screw (or longer)
At least 30% (Honeycomb or Giroid)
Support only from buildplate to support the first clamp fillet, it could work without but i have not tested it.