Well, actually that answered a lot.. Doing engineering and stuff is always fun. It's kind of sad, that probably you won't be able to use Rig'n'Roll for your purposes. Still, Nokrutnal's words tay truth - this is a game with it's own vision...
May I suggest searching for an alternative to test out your shifter? Like open source project Rigs of Rods. I know it won't come close to Rig'n'Roll in some aspects, but otherwise, it's highly customizable and trucks there have 10< gears

.
Well, we still can hope, that some sort of Development Kit, or sim upgrades would come out, but I wouldn't bet. In the end, the game will suit my needs
EDIT: ok, I haven't seen this page while writing reply (doh). My reply original was directed towards nicknackpaddywack. Nokturnal, you should stop these personal attacks. Your initial post was good, but don't let yourself to get carried away by it. Don't damage your reputation so much... Pook, and every sim fan. Well, sorry to get you tangled in here. So high modifiability patch is very wanted? We cross our fingers Nike-it :]