Years ago I came up with my version of this idea, and recently I converted my gang drill press to my adaptation.
Here it is:
I drilled the existing delta nut with twelve holes and created a new collar that slides up and down with a pin. The collar cannot spin, thus easily locking the nut.
here it is in place, but not locked:
and here it is in the locked position.
The delta nut is manufactured loose so it spins quickly. Each increment of the holes is approx .008, which is quite accurate enough for me.
Pete