Here is my design for the contest.
Filament Guide for Ultimaker 2 - Final version
This guide is used when the spool is rotated by 90 degrees behind the printer. The 90 degree rotation can be usefull force the filament ripples of the extruder to the side of the bowden and PTFE coupler. This mod helped me to get rid of a lot of underextrusions as the friction of the ripples inside the extruder was very high.