Yes, the Sansovino parking lot is outside of the ZTL area and would be perfect to then get on the tram to go directly to the SMN station. Open space lot, and often has spots open so need to book ahead.
Google maps doesn't place the marker correctly - the address is Via del Sansovino 53, Florence
It is south of the street to the left of the marker google does show - if you look at map at the top of the article here
http://www.visitflorence.com/florence-maps/parking-lots-in-florence.html
it is the first blue P sign after the 3 green P signs to the top left of the map.