There's no way to do this without some underlying forwarding... and aside from the obvious inefficiencies, bear in mind that any spam mitigation devices on the last hop that decide they are receiving spam are going to direct their wrath (reputation scores, blacklisting, greylisting, rate limiting, what-have-you) at the last forwarding hop, not at the origin.
We get enough collateral damage from legitimate voluntary forwarding already. I would shudder to think of mandated, irrevocable forwarding. Jeff
