I also wanted this effect. I will share the plan that I came up with, but as my cab is going slower than most (due to my inability to concentrate on anything other than alcohol during summer weekends) you may beat me to market!
I have kelsey's black skirted knob for a starting point. I am going to cut a 'donut' out of 1/4 lucite and buff the edges up. this will get mounted to the underside of the knob itself or perhaps I will bond it to the top of the cp (also covered) over the spinner mounting hole. Then, when I mount the LED under the knob the light will be 'piped' out and around the ring. Might need a couple of LED's to accomplish a uniform effect ('cause of the spinner shaft).
Now don't go usin my idea! (well not at least without a thankyou)
-C
oh, and hi kelsey!
ps. I like the balltop idea, I originally wanted balltops but was unable to find any, then ultimarc came out with the j-stick, but only in red! as my cab is all cool tones, the red was no good for me (black, blue, or purple would have been preferred). Also the j-stick was listed as having a really long throw, I ended up buying the t-stik from andy which has a short throw and I really like it, but I still would prefer that balltop.