How to add an element with a namespace prefix.

I have a very simple problem, but I think I am going about it the wrong way.

I have the following XMLTYPE variable in pl/sql:

<A xmlns="namespace" xmlns:def="myns_namespace">
     <B/>
</A>

In a separate step, I would like to add the following element after B:

<C attr="attribute" def:defattr="def_attribute"/>

To produce the following xml:

<A xmlns="namespace" xmlns:def="myns_namespace">
     <B/>
     <C attr="attribute" def:defattr="def_attribute"/>
</A>

What is the best way to do this?  I have tried the following:

1.  The following fails because when creating the C element, oracle complains 'namespace prefix "def" is not declared.  This makes sense.

SELECT
insertChildXML(
     eltA,
     '/A/B',
     'C',
     xmlElement("C", xmlAttributes('attribute' "attr", 'def:defattr' "def_attribute")),
     'xmlns="namespace" xmlns:def="myns_namespace"'
)
INTO ...

2. I've also tried creating element C with the namespace attributes before adding to element A and then removing the namespace declaration attributes using deleteXML.  This does not work because apparently the function can delete Attributes, but it cannot delete namespace declarations. I am trying to avoid ending up with this:

<A xmlns="namespace" xmlns:def="myns_namespace">
     <B/>
     <C xmlns="namespace" xmlns:def="myns_namespace" attr="attribute" def:defattr="def_attribute"/>
</A>

I was hoping to find a function that could do any one of the following:

1. Create element fragments, ignoring namespace prefixes and not throw an error.

2. Remove specific namespace declarations or any redundant namespace declarations.

3. Add a child element some other way in which the child element would not need to be created and validated independently before being added to the parent.

4. Or maybe I am going about this whole xml creation process the wrong way and need to rethink my strategy?