ACCORDING TO THE PLT, HE WAS ASSISTED BY A WING WALKER WHILE TAXIING TO THE TAKEOFF POSITION. THE WIND HAD BEEN INCREASING STEADILY DURING HIS STOP & IT CHANGED DIRECTION AS HE ARRIVED AT THE TAKEOFF POSITION. AS HE TURNED THE ACFT INTO POSITION ON RWY 27, THE RIGHT WING RAISED UNEXPECTEDLY. THE PLT ADDED POWER IN AN ATTEMPT TO CORRECT THE SITUATION & TAKEOFF; HOWEVER, HE WAS UNABLE TO CONTROL THE ACFT. IT TIPPED ONTO THE LEFT WING, STRUCK A DIRT BANK, THEN CARTWHEELED & CAME TO REST ON ITS LANDING GEAR ABOUT 200 FT FROM WHERE THE OCCURRENCE BEGAN. THE PLT STATED THAT HE HAD THE PASSENGER FASTEN HER SINGLE STRAP SHOULDER HARNESS PRIOR TO TAXIING. HOWEVER, AS THEY REACHED THE TAKEOFF POINT, SHE HAD REMOVED IT, COMPLANING THAT IT WAS UNCOMFORTABLE. WHEN THE PLANE BEGAN TO ROLL, THE PLT TRIED TO PROTECT HER & SLID FROM UNDER HIS OWN SHOULDER HARNESS. HE FELT THAT IF SHE HAD KEPT HER SHOULDER HARNESS ON, NEITHER OF THEM WOULD HAVE BEEN INJURED. HE REPORTED THE WIND WAS VARIABLE 230 TO 290 DEG AT 35 GUSTING 55 KTS.