This uses a Makita bit extension inside (diameter 11 mm, length 78 mm). 

For the attachment point at the driver, remove the mechanism from another attachment (in my case the offset one, see last picture).

Onshape Link: https://cad.onshape.com/documents/7c6fdd7ba10bb380f0eb286b/w/d3de6da449fb5e77dd0633dd/e/d9869d60525b19d01b83e6a3