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