Blah... Welp, dont look for help from me to do what you are asking. Although I will point you to http://www.sysadminmag.com/documents/sam0206l/ which describes how you can use perl and milter to modify messages as they pass through sendmail. It would be a simple task to create an anonymous gateway service using some of the email translation tricks listed there -- while still providing a valid respondable email address and backtrack route so as not to be so spam like (tm)..

-Waswas