Hi Jim,
Thank you for your suggestions, I had the same two solutions in my mind. I guess custom handler is the right way to go.
There is so little documentation about data objects in jbpm, so I was hoping I'm just doing something wrong and that it can be modeled the way I showed above (associating a data object to a task). I'm nor really sure what is the intended purpose of data object arfiacts in this case, since they don't make any difference in process execution, it seems that it is just a visual element for clarification of the process, but that's all.