Set up a t1.micro instance on AWS and run a VPN server on it. The VPN instance accepts connections on port 25, etc. and forwards it over the VPN to your home server.

Your ISP sees nothing but encrypted traffic between you and your VPN server.

Alternately, buy a rackmount server and colo it. Authorities would need a warrant to seize it, just the same as they would to seize the server that's running in your basement.