About exactly the same as freesco does, can also be done with BBIagent.

BBIagent is a also a single floppy Linux distro that does NAT for you. So get yourself an old box, with some RAM and a Floppy drive. You don't even need a monitor or HDD or CDROM.
Installation is easy.

http://www.bbiagent.com
http://www.bbiagent.net