its easy, you just open up a second NAT to grab a second ip, and a third, you just use seperate NATs for each ip, and then you can forward them seperately, like if your useing openWRT you can in the firewall where it says destination ip then you pick what ip is the destination, then point it to whatever internal ip adress you want, its really quite simple except for i dont know how to get a second NAT set up but any experienced linux user should be very easily able to walk you through it, just make sure that you tell them what kernel version you have, its different between the different kernel versions used by openWRT white russian and openWRT kamikaze