While I haven't used every type of twist on the bar-end throttle friction device. Or tried the big O-ring idea..
I really do feel the one the you can set with your index finger.. (it really does sit exactly where you will naturally push with your finger) is the best and easiest to use.
I had it inside my Tucano Urbano muffs earlier this year and it's not long enough to touch the top of the muff... I really don't wrap the throttle on all that much during normal riding.
I was not going to publish the model, as I figured it's too limited a market. (designed for the GS throttle, and Brake lever spacing), but I guess I will... along with instructions for having it printed with a 3D print-house.. (there are a few, and the cost is quite reasonable)
Stay tuned.
Also.. the two bits of Alu will work, as well as a piece of Polycarbonate, drilled with the correct size hole-saw, and cut up it's length. They are not rocket science.
Al...