From what I've seen, simple routers (from D-Link, Linksys, etc) usually don't have the ability to do advanced routing/NAT. Such things are probably supported on high-end (expensive) routers from Cisco, etc. Having said that, I don't know that you can forward the same inbound port to multiple IPs within a NAT'd LAN. The router needs to know which single IP to forward to, but inbound ident requests don't specify a target beyond the external IP of the router.