SAML using Form and specifying Format

I'm happy to see that SAML assertions appear to work in 4.5.1. Is it possible to set the Format attribute on the NameID?

For example when sent I see the following... and I'd like to set the Format to something else.

<saml2:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified" NameQualifier="Subject Qualifier">Subject Name</saml2:NameID>

At the moment I'm thinking the only alternative is to change to the XML WSS Entry type.