AFAIK the keyboard in question only uses USB for charging. It can't send keys over the wire.

That said, before getting the MX keys I bought a Dell 7440 keyboard on ebay for $20, fastened it on top of a 6mm clear acrylic plate with M3 screws, along with a Teensy chip running kbd firmware:

https://www.instructables.com/How-to-Make-a-USB-Laptop-Keybo...

Interesting idea.

If a keyboard has both wired-USB and some wireless technology, it's conceivable that physically disabling the wireless module(s) would be allowable.

I guess there are two possible hurdles: (1) getting permission, and (2) finding a keyboard in which I can disable the wireless module without causing too much havoc with the rest of the electronics and/or with the firmware.