Steph, I'm new to all of this, but if you ask Martineau for his WiFiVPN.sh script, it will do that for you. Once you've installed it in /jffs/scripts, I believe you would call it from /jffs/scripts/nat-start like this:
/jffs/scripts/WiFiVPN.sh MYWIFI_Guest1_VPN1 1
/jffs/scripts/WiFiVPN.sh...