i tried quantizing the slider output and to use the set message to immediately set the quantized value back into the fader for display, but didn't get any usable results.
Yeah, I tried that too, and the results are funny. I didn't quite expect it to work with a default "steady on click" slider, but I did expect it to work with a "jump on click" slider. The problem is that after clicking, when you drag, the "jump on click" slider behaves exactly like a default one.
However, have a look at the attached proposed workaround. I use two sliders one on top of the other, and take advantage of the fact that in Pd the gui object on the background catches mouse interaction, not the one on the front.
The main patch is "test.pd", while the other one is the abstraction used to control the slider. Look at the "send" and "receive" properties of the two sliders.
Is this an aproximation to what you were trying to do?