Just call a method of a Seam component. The Seam component can access the EM.
I needed to make the component Stateful too.
You will need to have the statefull bean set to session scope to be of any use, else it will no last between jsf and jbpm invocation.
The other way is to use process variables that are outjected on process creation and injected/outjected during the decision node invocation.
But make sure everything you try to put in that scope is Serializable.