From the item you’ve linked you’ve already got the female garmin mount so I’d start with something like this and then if I needed length to avoid my pack get a set of gopro mounts.
I also mounted the varia on my fatbike upside down so that the transceiver cleared the tire and the light at least shined on the ground, etc. It looked funny, but worked. I also thought that someone had a quarter-turn clip on mount somewhere. Don’t know how well it would work on a back bag as it was probably aimed at light usage.
How are yours snapping? Is it during rides or some sort of handling/tailbag access? I looked to be getting what you had originally posted, but maybe not now.
The Varia lights aren’t cheap - I’d hate to lose one.