I was thinking about the any% skip in where it skips the entire game. What if we start the vigilante mission to trigger end of the line but with some initial momentum just behind the polygon which teiggers the cutscene of the fire truck crashing. In this way the mission will be triggered and since CJ will move into the trigger for the last cutscene the game will load the last cutscene and end of the game. 
          I have no knowledge how the game works so please can anyone confirm this