Hi there. If you are willing to use the Drools Integration in jBPM5 there is clean and declarative way to do exactly what you want.
You can define a business rule that receive the events as Facts (conditions) and based on those events trigger one or multiple business processes (workflows).
I do exactly that in the Emergency Service Application that receive an event for each Emergency that it's generated in a city and triggers a business process to deal with that Emergency.
You can check out the code in the following Git repository:
https://github.com/Salaboy/emergency-service-drools-app
And read more about the application in my personal blog:
http://salaboy.wordpress.com/2011/01/01/emergency-service-drools-application/
Greetings
PS: this application was created in just two weeks so we are still refactoring it to show best practicies.. but there is a lot of things to improve.