Nothing that I am aware of, but it isn't very difficult to do it yourself.
Simply read the XML file into a stream, use SAX/DOM or StringTokenizer based algorithm to search and replace dynamic content and voila! you have the dynamic XML.
Perhaps a more detailed description of your problem can help me give you a better suggestion
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Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.