Hi Chris,
Since I hadn't done like that before. I don't know what will happened if we disable the DbSession.
If you want some documentation about have to create a process defintion programmaticly, I find some snippet from developer guide, I think it may be some help.
http://docs.jboss.com/jbpm/v4/devguide/html_single/#implementingbasicactivities
If you got some result, could you send some reply here? Thank you very much.