You could try a short length of rubber hose. Wrap the smaller shaft with tape or something to bring up the size a bit if necessary. Cinch the hose up tight with some hose clamps.
You might also try a coil spring for a coupling, if you can find something the right size. Or, maybe a light coil spring over top of the rubber hose.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)