No worries.
I took a closer look at the test cases in the jbpm-bpmn2 src and think I found what I was looking for,
Was able to get it working so I can plug in a process dependency simply by defining a new (or editing an existing) process with a <signalEventDefinition> in the <startEvent> node.
The BPMN2 eclipse editor does not currently allow you to add that element directly so I had to edit the XML.