Something like this should do it.
$game_map.start_scroll(direction, distance, speed)
Direction is 2 Down, 4 Left, 6 Right, 8 Up.
Distance is the distance in rectangles.
Speed is the same as the one in the command 1, 2, 3, 4, 5, 6.
Example:
$game_map.start_scroll(8, 5, 4)