I have seen some one-armed cyclists and they have mounted a thumbshifter on the bar top for the front and used STI for the rear. I guess you could use a thumb/bar end combo. Also, both of them did have both brakes tied together. One guy I saw, (he dropped me on a long climb) had a brace from his shoulder to the bar, I think so he could get low and still be stable. He was an excellent rider.