Take a look at http://hudson.qa.jboss.com/hudson/job/jbpm/lastSuccessfulBuild/artifact/jbpm-distribution/target/jbpm-5.3.0-SNAPSHOT-docs-build/jbpm-docs/html_single/index.html#d0e3990
jBPM 5.2 includes a UserGroupCallback interface that you can provide your own implementation for. There you can pretty much do whatever you want.
Hope this helps.