claim renewal url

I'm using saml:Assertion to represent a third-party claim. I have a set
of claim data that I've mapped onto the saml:AssertionType elements.
But, I have a piece of claim meta-data that's related to the claim, but
shouldn't be in the claim. It's the URL where an updated claim can be
retrieved from once the claim expires. This should be excluded for
increased privacy. Where could I put this? Is there an existing class
above saml:Assertion that I could put this in? Or do I need to specify
one myself?

John