Thank you. I realized that the original thread I referred to actually contained the answer. Day 8 in Mendix so I am still tripping over myself.
I am extracting the XML from the FileDocument in a Java Action.
InputStream fileDocumentContent = Core.getFileDocumentContent(this.getContext(), __FileDocument); String xmlString = IOUtils.toString(fileDocumentContent);
You can store the file into a file document. After that you could publish it to JMS with a java-action.