There are routers that will allow multipke IP's into the DMZ...but I suspect you need a static IP from your ISP...
Most ISP's, when establishing a static IP for a client will issue 5 static IP's...that is what MY ISP does, ATT DSL...All 5 static IP's come in on the same phone line into a 2Wire router...In the 2Wire, you can choose which IP's you want to NAT, which one(s) to send to the DMZ etc...
In my case, I took one IP and sent it to my web server, 2003SBS server, then I took one IP and sent it to another router, Linksys RV042 and NATed that for my LAN...
I plan to take another IP, send it to a second NIC on my SBS server for an FTP site...that would make 2 IP's in the DMS in my case...
Depending on how your ISP handles static IP's, and the equipment, you can do it...