We are attempting to super-turbo my altezza right now, however, the crossover point is proving to be extremely difficult. I have a japanese tuner working on it, but i am about to give up and simply install the turbo kit.
There are a few EK9's I have seen with it, and they are a kick in the pants, but for the GTR to incorporate it, you would need to add a bump or raised portion on the bonnet to fit the mechanisim itself into the vehicle.
Madmattgtr who is member of this board had a vortech supercharger he is trying to fit on his gtr with the t88 single conversion:
http://www.automotiveforums.com/markh/gtr%20pics/
If it all goes as planned, it will be crazy fast. As of right now he is putting 520 ps to the wheels, and he is really hoping for a better ET, and not really any more HP. He is going through Bee Racing in Tokyo for his work, so it should be interesting in the end.