In case you are still wondering about this, you can use the "WITH XMLNAMESPACES" clause immediately prior to the SELECT clause, and you can add as many namespaces as you need. An example would be:

WITH XMLNAMESPACES ('http://www.mynamespaceurl2.com' as "myprefix2", 'http://www.mynamespaceurl1.com' as "myprefix1", DEFAULT 'http://www.mydefaultnamespaceurl.com')

SELECT...

You then build the select and sub-select statements, using the prefixes you establish in your namespace clause in the AS clause of each field specification, such as "SELECT Field1 AS 'myprefix1:Field1'" and so on.

Hope this helps.