DDT - You'll also need the "half wheel" for the cruise control cable and the return spring (fig 6). You could buy all the cables from BMW that fit in the Bowden box but the parts start adding up and you would likely have to modify those parts to adapt to the Rostra cruise. Like the cable from the OEM Cruise half wheel what I'm calling figure 6...the cable from BMW back to the Rostra or slack tube would likely have to be modified to connect. I was trying to do this as "professionally" as possible without breaking the proverbial bank.
It looks more intimidating than it really is. The best time to do this mod is in the off season when you are not riding much. And if have a friend or two that will "hold your hand" it makes it much more enjoyable. I had a riding buddy that also has a GS. Though he is not technical it was a comfort to have him there supporting me while I cussed when things went south!
Another good friend to have on hand for this project is Mr. Crownonice.
Just call on him sparingly...
or you might find your newly installed cruise control stuck on WOT at a most inopportune time.