Lines or Arrows to show completed or finished tasks!

Hi,

I have some tasks with outline level (1 and 2).And the gantt chart is as shown in the below picture.Is there anyway to show arrows or any other symbol to highlight the completed or finished tasks.

existing gannt chart

http://i57.tinypic.com/4htg74.png

required output

http://i61.tinypic.com/29mtvza.png

Can this be done programmatically?

Thanks.