I picked up a foot of 1/2" Delrin rod at Tap plastics today and had a semi proper stab at making the magnetic holder work.
It works! It picks up the nozzle with a satisfying click and the release force is not excessive, but much more than any component I'll be picking up.
I do need to refine the machining process as the run-out is terrible and all at the stepper side as far as I can tell. However I only used 1" of material at 21c per inch, so I can have a few more tries. A cheap set of metric reamers are on order, and I'll be making up a collet to hold the piece out of Fortal alloy I have lying around. Holding a hollow piece of 1/2" Delrin in a 5" 3-jaw chuck tightly enough it doesn't slip distorts the heck out of it I think.
Final drills used were #11 on the stepper side and K on the nozzle side. This gave a close sliding fit on both ends. Friction on the stepper side provide by jamming it over a Kimwipe. Oddly the local stores do not sell metric drills. Or reamers.
A quick manual test-suck reveals functional vacuum seal and pick-up capability.