There is one connector below driver seat, with 8 PINs. It's described in the BEMM manual. It should be called "vehicle interface connector" or something similar (I have the Italian version, not sure about the original name).
PIN number 3 can be used to permanently disable the stop-start and smart charging. If I'm not mistaken, you can connect this pin to gnd to disable S&S.
To ease your search, one of the other PINs on the same connector provides the "engine on" signal and is used in the split charge system to connect service batteries on camper conversions.