Man, people are making a huge deal out of something so easy to fix/hide. Unless I'm missing something very subtle that differs in the way this new knob is supposed to work.

The fascia currently fits over the knob. It currently covers up a portion of the knob. Put a hole for a set screw as far back and as small as possible so it is completely hidden when the fascia is put on.

What else would work... A small piece of rubber placed on the flat part of the stalk creating a firm grip when the knob is attached. Likewise, a small flat piece of metal, no wider than the diameter of the stalk, bent into a V shape and placed with one of its sides attached to the stalk (open end toward empeg). Then slide the knob on for a firm fit (if the V piece was made properly - you could also slot a little into the back of the knob after it's been turned (on the lathe, not by hand on the stalk :)

There are also other ways of making the knob - in multiple pieces for instance. Though it would be a little more work to have it all fit together nicely.

Oh, and there's always looking at other metal knobs out there on other products to see how they do it. :)

Bruno