I know this is probably a long shot but..........................
Could I retro fit the Cruise Control K64/17351 Ü to the bike and be lucky enough that all the required gubbings are already wired into the bike to make this work by simply fitting the switchgear?
Far as I know 1150RT's never came with electronic cruise control so simply plug and play would not be possible, google throws up some options of fitting an electronic cruise control but looks complicated long winded and expensive, either buy a R1200RT with cruise or look for one of the many "Throttle Lock" options
I had an 03 1150RT and it didnt have cruise control. I fitted a Wunderlich throttle lock which worked brilliantly and once you get used to it is very easy (and safe) and makes a huge difference. I highly recommend one of these as a very cheap and easy solution. NIppy Normans sells them (as do others I expect)
I, like puggy went the manual route. I actually made my own throttle lock which worked really well. Of course the manual ones wont hold speed, only throttle position. So, any inclines or declines will result in change of speed. Not a big deal for the most part.
However, to the OP's post, I personally don't think it will be a quick plug and play solution.
I was interested because I may be in the market for one and would be great to have factory cruise, but nowhere on the internet can I find any confirmation of the of R1150RT ever being fitted with cruise from the factory, there is plenty of examples of people asking the same question and each time it has been confirmed that R1150RT's never had factory cruise.