Using custon namespace with SignedXML

I am trying to use a custom XML Namespace in the signature node in a XML signed file with C#. Following Microsoft's example (http://msdn.microsoft.com/es-es/library/system.security.cryptography.xml.signedxml%28v=VS.8开发者_JS百科0%29.aspx), I was able to sign the file without problem.

But the generated Signature node is not inside any namespace and I don't know how to add to the generated Signature node the desired namespace information. Should I go through XSD transformations or does it exists a simpler way to specify a prefix to the generated Signature node (and child's nodes too)?