If you add sprite for the line and set it's origin to the right, and have at least one instance, this would work:
sprite: picked top instance
system: compare distance(Mouse.X,Mouse.Y,Sprite.X,Sprite.Y) > 48
---system: create sprite at (sprite.x,sprite.y)
---sprite: set angle toward (mouse.x, mouse.y)
---sprite: move forward 48 pixels