Michael, I got pulled into another project and haven't had any chance to look into that in more detail. I've chatted with the jBPM guys in their IRC channel (http://irc.codehaus.org/, then select #jbpm in the channel dropdown), but still couldn't solve that problem.
I only got a small step further and finally managed to connect everything to my mysql database, although that raised a bunch of other issues.
I also need a solution to that pretty soon as the current project is supposed to take advantage of jBPM too... Honestly, I've started looking into Activiti (http://www.activiti.org/) as an alternative if there are more obstacles with jBPM.
Cheers,
Mike