I have a linksys router with dd-wrt installed on it. I have tried script after script people have suggested to allow for multiple static ips from my ISP (small business internet). I can not find one that actually works here is an example script for the second of 5 static ips that got me the closest. This will at least direct the external ip (68.115.xx.xxx) from an internal connection to the machine however it still doesn't work from an external connection.
/usr/sbin/ip addr add 68.115.xx.xxx/29 dev vlan1 /usr/sbin/iptables -I FORWARD -d 192.168.0.52 -j ACCEPT /usr/sbin/iptables -t nat -I PREROUTING 1 -p all -d 68.115.xx.xxx -j DNAT --to 192.168.0.52 /usr/sbin/iptables -t nat -I POSTROUTING 1 -p all -s 192.168.0.52 -j SNAT --to 68.115.xx.xxx