I've already explained how:
"you can have two different persistence units.. one for the JPAKnoledgeService and the other to the minaTask Server in this case. That will allow you to configure different databases for the sessions and for the tasks."
Probably right now you have a single persistence unit that includes the SessionInfo and ProcessInstanceInfo entities plus all the Task Related entities. You can basically create to different persistence units and configure different databases for each of them. All that configuration is related with JPA and HIbernate, it is not really dependant on jBPM5.
Cheers