I had a couple of goes at implemeting this on a different question:
http://forum.plantuml.net/8983/how-add-exception-line-group-items-plantuml-activity-diagram

Above looks a bit more like the example, but the below is #better UML I think uising PlantUML:

Click through to see and edit the code - but mostly it's the 'interruptingzigzag' sprite that allows this:
sprite $interruptzigzag [16x16/16] {
0000000000000000
0000000000000000
0000000000000000
0000000000000000
000FFFFFFFFFFF00
000000000000F000
00000000000F0000
0000000000F00000
000000000F000F00
00000000F00000F0
0000000FFFFFFFFF
00000000000000F0
0000000000000F00
0000000000000000
0000000000000000
0000000000000000
}
I hope that helps, and post an example of how you make it work?