Not feasible. For that to happen the CIA agent would have to stand, lift the gun up into open view, and fire right over the head of the driver and the other CIA agent in the passenger seat. It would have blown their ear drums out.
That’s EXACTLY what happened. After Oswald fired off his two or three rounds, the Secret Service agent raised his AR-15 in response JUST AS HIS VEHICLE LURCHED FORWARD to follow the Kennedy vehicle. His trigger finger pulled back as his car leaped forward in panic, and BLAM! I believe this was a million-to-one odds accident but entirely plausible given the intensity of the last head shot.