iRule to add Sender Vouches SAML Assertion to SOAP Header

I am trying to add a Sender Vouches SAML assertion to a SOAP request that is coming into F5. I don't believe there is any native way to do this (If I am wrong about this, please correct me), so I am trying to use an iRule to embed the assertion into the SOAP header and sign the SOAP body.

Has anyone else ran into this same requirement?