Xerces C++ SAX: How to capture an element as DOM?

We use the Xerces C++ SAX parser for parsing XML documents that have a specific form, where the only possible element tags are

<m> <l> <v>

These stand for "map", "list", and "value". As such, it defines a form very similar to JSON. The details of the encoding is not important for this question. The real question is, I want to add a special node:

<x>
    ... any valid xml document...
</x>

If we were using the DOM parser, this would present no problem. But since we are using the SAX parser, I don't want to process every element and attribute inside the <x> tag explicitly. Instead, I would rather ask the parser "please give me the DOM for everything inside the just-opened element (i.e. inside <x>)".