If you just want to move the sets backwards, but not up, then I think you need to have some jack-up-plates custom fabbed. And will need a longer gear change rod also.
Here's a sample of the part Decosse mentioned:
http://www.torquespecialparts.com/20...d-triple-1050/
If you have big feet, you can also just move the pegs with the GSG Varios and leave the rear sets where they are: