I have finished documenting and putting up on my website what I call AmprNAT. For those who attempting to get out via amprgate sourcing as their lan IPs, this not only will prevent this from occurring but also it will NAT you out as your gateway's IP... pending you're using a distro of linux. It requires a static route in your route pointing to your gateway, and then 3 lines of iptables rules.

You may read about it at: https://n1uro.ampr.org/linuxconf/44nat.html

I believe Lynwood is adding info on the wiki for this.