My take on the Printrbot extruder mod for NinjaFlex filament.
Print with .2mm layer or less (to get a cleaner 1.75 hole).
No need for support.
If the filament does not extrude adjust the screw on the extruder arm. It may require more pressure to push the filament.
No need to disassembly the extruder, just make sure the filament is through the hole and use the extruder motor to get it into the hot-end.
With this thingy, I can print at 30mm/s without the filament getting tangle into extruder.