Sequence Diagram in UML

[John Tsangaris <johnt webevent com>]

I am trying to make a sequence diagram in Dia, but am having a hard time 
find where to create additional control boxes.


  Object
---------
    |
    |
    |
    |
    |
    |--    # This one appears with the lifeline object
    |  |----------------------------------------------->
    |  |
    |--
    |
    |
    |--    # This one is non existent.. and I can't find where to get 
another one.  
    |  |<-----------------------------------------------
    |  |
    |--
    |
    |
    |



Does anyone know how to add additional control boxes to the lifeline?


TIA


-John