I don't know where the BIS Get In script is located, but if find it, it'll probably better to use since it doesn't let you get into position unless you are on that side door.
Patr = Patrol addAction ["Get In Driver", "GetIn.sqf", "DRIVER", 1, false, true, "", "driver _target == objNull"]
It will only appear when you are close to and facing the vehicle, it won't appear if there is already a driver.
GetIn.sqf
private ["_veh", "_player", "_action", "_seat", "_getout"];
_veh = _this select 0;
_player = _this select 1;
_action = _this select 2;
_seat = _this select 3;
_player action [format["GETIN %1",_seat],_veh];
call compile format['_getout = _player addAction ["Get Out", "GetOut.sqf", [], 1, false, true, "", "speed %1 < 10"]',_veh];
GetOut.sqf
private ["_player", "_action", "_veh"];
_player = _this select 1;
_action = _this select 2;
_veh = vehicle _player;
_player action ["GETOUT",_veh];
_player removeAction _action;
I don't have my ArmA to test this out, so please report any RPT errors.