XO-1 spur-to-pinion adapter that includes the "Cush Drive"?

[Lizard]

Dremeling a spur until it looks like the drive-key? That's ambitious :)
Where will the base fit then? I think there is no space inside the spur assembly (?)

Maybe make a CAD drawing and have it made by some CNC service. An M3 screw in a 4.5mm wide drive-key should be no big problem I think. The hole would have to be 2.5mm, that leaves a mm on each side. Even M4 could be okay considering that the drive key is 5mm wide near the center. 3.3mm hole would leave 0.6mm at each side at the top and 0.85mm near to the center. But that would probably require good material (not brittle and also not soft). Or use M3.5, but screws and taps are hard to find for those.

Or maybe go to a local machine shop or something and have them drill a hole into the motorshaft so that you can use the pin to mount it.