I've been wondering the same thing (is there a plugin already?). I couldn't find one but haven't been looking for it very hard at the same time. I did however been planing to write one as it seems easy enough to do. Unfortunately I can't find any spare time at work to do so (as we're only evaluating jBPM 4.4 at the moment).
But would very much like to get my hand on such plugin. So, anyone willing to contribute? :)