UPDATE OCTOBER 2012:
The original blog is not existing any more.
I did a recent article that covers this in detail: Tutorial – NUnit and Sequence Diagram Recording in Enterprise Architect 9.3
More posts on similar topics can be found here: http://blog.lieberlieber.com/tag/sequence-diagram/
I found a nice “blog” Post how one can build sequence diagrams from “code” using Sparx Systems Enterprise Architect debugger and Sequence Diagram recording features.
Auto generating a sequence diagram from code
Currently we are looking in doing similar stuff for future Versions of LieberLieber AMUSE. In our current implementation for Activity Diagrams we use the object model and not the debugger to record the sequence diagrams.