the ecu already knows what gear the 6mt is in, it calculates the gear by knowing the speed of car and rpm.
however you actually have to get the car to move first before the calculation takes place.
forget about getting the screen to display the gear, its way easer just to have your own display up there. IE a few leds

messing with the cam system and modifying the ecu like that will be VERY hard. you will need the source code of the ecu and will have to know machine code.
the reverse engineering of it and R&D could take months.

 

^+1 if someone goes through with it, it would be better to have leds or small lcd display separate from center display for easier install. While it seems highly unlikely for anyone to try all this i am nearly certain that in sometime in the future i will find a thread saying "6MT gear display!" ....

 

LEDs...no thanks.
I'll look more into it though. I'm never convinced by the "it'll be too much work" argument.