Here's the solution for Ubuntu and likely other distros. I gave myself a big slap in the head when I saw how dumb I was.
Add the following line to /etc/modprobe.d/options
options usbhid quirks=0x046d:0xc71f:0x00080000
(which we knew already)
reboot or rmmod usbhid and modprobe usbhid. The update-initramfs isn't necessary when manually modprobing the module.
Since the usbhid driver loads from initramfs, unless you update it, it just ain't gonna see it.
Enjoy your mousepad. Works great for me