Finally found some time to take a try with what I described, so the process would look something like this (it does not address all the requirements but just illustrates how it could be used):
http://community.jboss.org/servlet/JiveServlet/downloadImage/2-633171-17217/450-332/process.jpg
Process was drawn in BPMN2 eclipse plugin so most of it was possible but few elements, like timer duration, need to be done directly on xml.
I have managed to run the example and it was interupting the sub process when signalled so it seems like it could be rather nice alternative to more complex options given above.
Unfortunately signal event is not implemented for boundary events, small modification to jBPM code is required.
Please find attached complete bpmn definition for reference.
