I had a Throttlemeister on my first FJR and I liked it, but put a Vista Cruise on the next and it was just as effective, simpler, and much less expensive. Both hold your speed for long enough to use your right hand for something else for a minute or just stretch out a cramp. Neither really maintains your speed like a cruise control, as I'm sure you know. But simple can be good.
Can't seem to attach the link--just do a search. Amazon has them for about $25.