Support for Reusable Sub-Process in jBPM web designer

A reusable subprocess node would reference an existing BPMN2 process. Currently a dedicated node type exists for this purpose in the Process Designer plugin for eclipse. This would be modeled as a "Call Activity" in the BPMN 2.0 XML and have the ability to map variables back and forth:

<callActivity id="_4" name="Sub-Process" calledElement="ChildProcess">
<ioSpecification>
<inputSet>
</inputSet>
<outputSet>
</outputSet>
</ioSpecification>
</callActivity>

The web designer already has a checkbox for "is a call activity" when an embedded subprocess node is created but this checkbox does not affect the BPMN XML.