Front-channel AttributeQuery Profile

Hi, I'm considering whether it is reasonable to make an Assertion/AttributeQuery profile that allows front-channel bindings...

I'd like to exploit the possibility of implicitly referring to the current user (as things are front-channel), and therefore I am abit stucked because the AttributeQuery extends SubjectQueryAbstractType (if I remember correctly), wher a Subject MUST be included. in the use case I would like to solve, the SP and the AttributeAuthority does not share a common reference to the current user...

Would it be a good idea to omit the NameID, and use Subjectconf as sender-vouces or bearer... Something like this? Better ideas appreciated....

<AttributeQuery xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

 xsi:schemaLocation="urn:oasis:names:tc:SAML:2.0:protocol saml-schema-protocol-2.0.xsd"

 xmlns="urn:oasis:names:tc:SAML:2.0:protocol"

 xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"

 ID="_d7607d551380ac97853a6ff4907c4ef01219be97dd"

 Version="2.0"

 IssueInstant="2008-05-27T07:46:06Z">

    <saml:Issuer>http://rnd.feide.no/sp</saml:Issuer>

    <saml:Subject>

        <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:sender-vouches" />

    </saml:Subject>

    <saml:Attribute Name="urn:oid:2.16.840.1.113730.3.1.241" />

</AttributeQuery>