Someone has made a custom controller for the HHKB Pro 2. I'm not sure if it would work for the Pro JP though...
Yeah youll have to make another custom controller for the JP due to the extra keys, but it shouldn't be such a big problem.
I don't imagine that to be the case. The biggest problem would be whether they're compatible or not. If they are, I would imagine you could just write more code to get them to work.
But what do I know!? I'm a damn moose.
Mooses don't talk. They growl untill they end up on the table. Sweet, delicious baked moose testicles..
Back on track: You're indeed right, a compatible chip would be needed. BUT what you need is what type of chip is used inside the keyboard, max voltage it can handle (and which it uses), find a "similiar" one, program it, add resistors/whatever you need to add to make it functional inside the board, run it and bam you'll have an amazing Topre keyboard that can beat the **** out of every moose there is in the world. No offense mooses.