Support the FIXML protocol (FIX 4.4). There is both a DTD and XML Schema based format.
A possible strategy is to use a XML binding tool like Quick that can process both XML schema and DTDs. The XML would be transported using normal QFJ sessions. The XML body would be converted to Java object that could be used by an application. The downside is that these objects would be different than tag-based QFJ FIX message objects. Ideally, we'd be able to provide the same message objects whether the message was tag-based or XML but there are some subtle differences between the two formats that make this more difficult than it might be (e.g., the way components are used).