That charge light on the side...
Wow! was really happy to find this thread! I have a 1981 BMW R100RS that I've converted to a Cafe Racer.
I recently ordered the ACEWELL speedo because the big old plastic ones are horrendous and the originalspeedo was inaccurate. Your post got me 95% of the way through the installation, but I couldn't get my mind around having to install the charge light separately, so I roped in a mate of mine who is a car electronics propeller head and he provided me with a simple way to use the LED in the ACEWELL speedo rather than the work around you have suggested.
We simply wired in a relay to replicate what the bulb would have done and it works perfectly. If you need a diagram and pictures, I'm happy to supply them.