jBPM and graph oriented programming are the best basis for implementing new graph based execution languages.
from this definition http://office.microsoft.com/en-us/assistance/HP010575031033.aspx it seems that EPC is actually a graph based execution language. So that is exactly what jBPM and GOP are intended for.
EPC is a process modelling notation rather than a language. From what I can grasp from a 5-minute review, it can be paralleled to a UML activity diagram if you rename states to events and activities to functions. Furthermore, EPC provides explicit elements to represent organization units and resources required to better model business processes. See the Wikipedia entry for EPC for more detail.
There is a standardization initiative within the EPC Community focused upon development of an Event-Driven Process Chain Markup Language (EPML). OASIS is the standards body hosting that effort; read more about it in the cover story. EPML is said to be motivated by the goal of supporting data and model interchange in the face of heterogenous BP modeling tools, which was more or less the same motivation behind XPDL, the language endorsed by the Workflow Management Coalition. However, unlike XPDL, EPC has some big names behind it.
Given that jPDL is, to some extent, an execution language for UML activity diagrams and the parallel outlined above between those diagrams and the EPC notation, I can say with confidence that a EPML extension on top of jBPM is both feasible and easier to implement than a BPEL extension (as BPEL is in a separate domain).