Hi, newbie question here.
Is it feasible/costly/possible to fit cruise control to an LT that wasn't factory equipped with it?
Having done a lot of work / tests / troubleshooting on these BMW cruise-control systems, I would say it is not cost effective, neither easy to retrofit.
It was NEVER intended to be retrofitted outside the factory as even the main wire harness is not the same. In addition to Left-handlebar-combo-switch, you would need a cruise-control unit (hidden under fairing) and a lot of home made wiring to compensate for changes in main wire harness. And to add to complexity, there is a change needed to the throttle-body assy for the 3rd throttle cable (between cruise-unit and throttle-bodies).
Of course nothing is impossible.... BUT unless you are very talented with wiring, have a lot of patience and money trow at this problem, I would say it might be easier to sell yours and buy a K1200LT with more options.
In summary, you would need:
1) A different Main Wire Harness ..OR.. many added wiring jobs yourself (mainly from brake switches to left handlebar switch to cruise unit)
2) A cruise-control unit
3) A different left-hand switch assy at handlebar (included high-low beam and horn)
4) A different throttle-bodies assy
5) two new throttle-cables
Even if you get all these parts USED cheaply on EBAY, you will need many hours of fun, work and testing...
No dealer has ever done it because BMW told them it was a "factory installed only" option AND because doing above would be very time consuming at $85 / hour at dealer (my rough average of hourly rate).
Sorry for the reality check ;-)