I used to work at a spam company and we did this and similar techniques. One similar technique was we basically created our own fake ISPs, disguised as rural w

I used to work at a spam company and we did this and similar techniques. One similar technique was we basically created our own fake ISPs, disguised as rural wireless Internet providers. Paid yearly ARIN fees, had or own /20 blocks of IP space allocated, etc. We specifically requested ip filtering completely removed from our peering connection with major upstream/backbone ISPs. They did so without question. This allowed us to source route any IP out to the Internet. Then, we would purchase large blocks of IPs (a couple of /20s a month) from Romania and Argentina. We would create GRE tunnels over to RO and route them back to the US. It's been years since I was involved so my memory of the technical details is hazy now...