I don't suggest you to go to the binary format or the API's I suggest you to create an xml parser for the ego format that I think that you already have and then just using that parser write BPMN2 xml format. Then when you get the BPMN2 xml file you can just load it inside the jBPM5 runtime. In that way you keep your parser agnostic of the execution environment and not just you can use that parser.
Cheers