Success! This is certainly a niche issue, but since it’s taken a pretty lengthy amount of research to resolve, I thought I’d add some resources here in case it’s helpful to anyone else.
After exploring others’ recommendations, I’ve saved hardware solutions for tinkering in the future and was also not able to find a way to temporarily disable mouse movement through gnome. I finally landed on python-evdev as my solution. With this, you can read input from one or more devices simultaneously, create a virtual input device to write events to on-demand, and (maybe most importantly) retain exclusive access to the original hardware devices to absorb their input. I’ll also shout out evsieve which lead me to python-evdev. The python-evdev documentation is quite thorough, and it’s quite a custom solution based on your own needs, so I’m not going to go into great detail on my python script - but it’s only 27 lines long, nothing major.
Be aware that you may need to write some udev rules to allow access to the physical devices and to allow the virtual device to be created. This was the easiest part for me to find help with, so I’ll leave some abridged copy/paste details below:
Find your device Vendor and Product IDs
cat /proc/bus/input/devices | more
Write a udev rule (I used priority 71) to allow access to the device:
SUBSYSTEMS=="usb", ATTRS{idVendor}=="", ATTRS{idProduct}=="", TAG+="uaccess"
Add a very poor udev rule to allow a virtual device to be created by python-evdev (there’s probably a much better way to do this):
KERNEL=="uinput", SUBSYSTEM=="misc", OPTIONS+="static_node=uinput", TAG+="uaccess", MODE="0660"
We’re just air conditioners