***Update- I'm re-releasing this under the GPL and including the source files.  This last model has a few small improvements as well.  This part was modeled in SolidWorks2018.  Thank you for all the interest!
Long bowden tubes suck!  This was even more apparent after installing a volcano clone heater block on my printer.  You need precise control of the filament to keep blobbing in check.  
Try this experiment-  print out one of the many manual extruder knobs here on Thingiverse and install it on your extruder.  Make sure the filament is fully inserted in your nozzle, and cool down your hot end.  Once it is cool and the filament is fully fused into your hot end, turn the extruder knob back and forth and see how much the filament can move at the extruder with no movement at the hot end.  The longer your bowden tube, the worse this is.
After looking through Thingiverse for a decent direct drive conversion for my CR-10 and not finding anything I liked, I decided to model my own.  This fits on a stock CR-10 using…