Following the asking of this question once more in XML-DEV, Rick Jelliffe has posted an answer suitable for inclusion in the FAQ.

The short answer is: "You must use a stream of XML documents. The simplest way to do this is separate each document with ^L, which is not an allowed character in XML and which is not used for in-band signalling by common streaming systems."

For a fuller discussion of this topic, see Rick's posting to XML-DEV.