Apparently, Ferlib more recently produced a double trigger that allowed for this on their sxs:
One very interesting innovation was that most of the double trigger boxlocks had a feature whereby the front trigger will fire the right barrel and when pulled again will fire the left. It sounds complex, but when I questioned Ivano about the details, he assured me that it was not complicated; and proceeded to prove it by stripping one down to show me, and sure enough it wasn't. although he certainly makes best guns, Ivano is very much of the opinion that they do not need to be complex; simply very well finished. Simple ideas are the most reliable, and that is one of the qualities inherent in a Best Gun.
