I should be able to do it with the REST interface.
I think that the documentation for jBPM 5 should be reconsidered. As a user of jBPM5 I will probably not have much use for knowing how to instantiate the KnowledgeBase, KnowledgeSession and so forth. It appears that jBPM5 user API is the REST API. That doesn't seem to be covered very well in the jBPM5 documentation.