How to add more than one execution specification on sequence diagram using Dia Software

I'm using Dia to make a sequence diagram and I need to make a lifeline with two (or more) execution specification, like the image below:

(What I want is inside the green circles)

How can i do that?

You can simply stack two Lifeline elements on top of each other. The top of the second lifeline can be connected to the end of the execution (the grey area) in the first lifeline.