I'm afraid that what you're trying to do is impossible with the current implementation. If you use an attribute for the naming scheme, the function <i>title</i> of the attribute's datatype is called. In case of an XML block, it will return <i>eZXMLTextType::rawXMLText( $contentObjectAttribute );</i>.
Beside that, I doubt that using an XML block for the title is a good idea.
