In theory it should be possible to translate a BPEL process into a BPMN2 process so you can execute it on jBPM5. There should probably be a 1-to-1 mapping of BPEL elements to their corresponding BPMN2 construct. There has been work to translate BPMN2 to BPEL, not sure their has been a lot of work in the other direction. But I think it shouldn't be too difficult with an XSLT transformation for example.
I would suggest definitely searching the internet to check whether no-one has already done this work for you, as I imagine someone might, as it could be useful in a broader context as well.
Kris