I never used the audio from my 550 on the bike. All the time with the car mount.
For the bike install, I used the ball mount that came on the GPS packaging.
I drilled and tapped the ball mount. For 1/4 20 threads. I had that size all thread on hand. Next, I removed the rubber plug from the top of the triple tree and lowered the all thread / ball mount into the hole.
Pad the top of the fender to avoid scratching. Better yet remove fender.
Measure the excess length of all thread sticking from the bottom of
the tripple, then cut to allow a little of the all thread to show below the bottom. Remember to have a nut installed to chase the threads of the all thread before cutting.
I also filed the bottom of the ball mount to match the square hole of the triple.
A 1/4 in deepwell socket worked well to tighten the nut on the all thread below the triple.