Cool, use the Dumas dog bone and brass.
However, usually this type setscrew shaft coupling have to be customized. like below coupling:
<a href="http://www.fscoupling.com/18-inch-to-3mm-helical-set-screw-coupling-18x3mm-cnc-motor-shaft-coupler-diameter-16mm-length-23mmneed-customized-p-218.html">1/8"x3mm coupling
</a>just as you say, it have to be two bore to connect the each side. one bore is not useful.


-luso