The behavior that you describe is correct, that is you invoke fireAllRules() before the process reached the business rule task and so at the time you invoke fireAllRules() there aren't any active rules.
A simple solution is to add an EventProcessListener to the StatefulKnowledgeSession and then for every ProcessNodeTriggeredEvent, if the node is a business rule task, call the fireAllRules() method. But if you using jbpm-console to run the process I don't have any suggestion because i don't know how to manage the StatefulKnowledgeSession incapsulated in jbpm-console.