Sorry for late response. The system is upgraded and we don't have much notification. My suggestion is to:
1) Write an class that implements StreamSource
2) Add the webservice method on it. According to your description, the webservice is a provider instead of a client, please refer to the docs on how to implement a WS provider at OEP.
3) If needed, implement RunnableBean to start the webservice.
4) Assemble it with other stages and take this class as adapter