I use it with the standard mount. It’s not the easiest to coax out, and mounting is fairly crude (a couple of zip ties which need tightening every now and again) but it works. I used the lanyard initially for added security but stopped bothering after a while as it seems fairly secure.
I just got a D20 last week and I have 5 bikes, so there was no way I was going to spend £50+ on mounts for each one. I had been using these previously for holding smaller flashlights on my bars and it now works perfectly for holding my D20 on the stem. I also use a couple of blobs of blue tack top & bottom to help secure it.
It is basically like using a couple off (strong) elastic bands, I did need to take my stem off to put them on the bikes though.
You can get them through ebay too if you don’t want to wait for ever for DX to deliver!
Here you go. You could probably get the same result using strips of inner-tube, but Im not sure if they would be too tight, plus you would need them pulled towards the centre under the GPS so they wouldn’t slip off.
The silicone is just right between stretchy and tight enough, the extra bit (clear) is just one cut in half just in case, but there is really no need for it.
The wrist strap is wrapped around the stem though.
The blue tack is needed so it has something to make it grippy, and it really works well.
If you were wondering, the stem is a broken adjustable that is carbon wrapped so i can use it!