You should try shifting the Vittoria without clappers. Same method to throw the lever forward to slacken the chain. Then you use your fingers to move the chain sideways to a different cog while backpedaling then tension the chain up again. I tried it and thought I would die in the process. I got it to shift a few times that way but feared for my life. You really have to be going slightly downhill to pull this maneuver or you must dismount if you intent to climb and change gears. The dirty fingers are the least of your problems when shifting with that mechanism.
Ray Homiski
Elizabeth, NJ