I'd just like to say that not only is that solution free (to the end user), but it's an excellent solution. I even like it better than the keyed shaft in the Mk2as, as it makes it that much easier for me to machine a replacement knob, once I get around to it, so that I can actually grasp the damn thing.

Edit: I realized after posting that it sounds somewhat as if the major reason I like it is for easy replacement. That's not true. It works 100% of the time with no issues whatsoever. The replaceability is just icing on the cake.