After growing really tired of Solaar freezing, forgetting to apply settings, being crap, and currently simply not working on my system, I tried libratbag which is absolutely terrific, apart from not working with my mouse. Or rather, it works, but this mouse doesn't have non-volatile storage for settings, so it resets to default settings when it goes to sleep after not having been moved for a couple of minutes.
This terrible hack simply writes a handful of bytes to the correct /dev/hidrawN node
everytime udev notices something with the USB PID and VID of this particular mouse
has come online.
The "handful of bytes" is basically just taken from ratbagd's debug output
(which is also a pain to get to, because of the awfulness that DBUS is. God, I hate DBUS.)
I've made very little effort to understand the protocol, apart from resolving a few magic numbers and some structure from the libratbag HID++ 2.0 implmentation. (The files with names like hidpp20.c in libratbag)
As I've just hardcoded some (probably setup specific) values, it'll probably not work for anyone else. When it breaks, I just might look into actually implementing the necessary part of the protocol in a slightly less stupid way.
Pretty much all the effort I've put into this has been getting udev to do the right
thing. Which resulted in the wrapper shell script, because udev is a complete pain.