According to "The Nikon Manual" you should be using the three finger maneuver. Thumb on film advance, index on shutter and middle for focusing, NOT.
My S2 is easy enough to focus with the wheel but you can use the focus ring if you wish just make sure that you have the infinity lock off when you do or you could break something.
As far as the recommended three finger approach, I don't use it.
What lens are you focusing? Too heavy a lens will do a number on you finger.
I love the three finger grip. Out allows me to focus a 50 or wider, fire the release and wind with one hand while I have an off camera flash on the other. So much faster than with Ms and a 'Cron or CV lens.
Index finger for shutter, thumb for wind, and middle finger for focus. Much better leverage IMHO.
Well, in fairness, I am shooting a Kiev 4A with a Jupiter 8 which I imagine is not nearly as smooth as a Nikon rangefinder at focusing. I have tried the Contax grip and am not a fan. I prefer focusing with my left hand which is what I have to do with all my other rangefinders and SLRs anyway.