Is it possible for you to add something like " http://firstname.lastname@example.org "? I can't really find a way of testing it?
I'm not sure excactly what you're asking, so I'll give you a somewhat general answer.
There's a few ways you can use a link with an email parameter for unsubscription.
One is already built into Campaign Monitor:
test = your client subdomain
123456 = API List ID
email@example.com = the address, obviously
If you want to use your own domain, like your example, I'll give you a couple possible solutions:
Either: Set up a server side script at http://www.siteastic.com/unsubscribe that reads the email parameter, and forwards the subscriber to the url described in the first example (which, in turn, forwards the subscriber to a confirmation page).
Or: Set up a server side script at http://www.siteastic.com/unsubscribe that uses the API.