I think the setup would only work if you knew the source address/network where people were connecting to each of the public address.
If you knew that network 184.108.40.206/24 would connect to IP1 and network 220.127.116.11/24 would connect to IP2 you could easily configure a Policy NAT
Is it possible for you to list the services (TCP/UDP port numbers) that need to be reached from the Internet for each of the servers that have not yet been combined?
Can you also mention the software version running on your firewall? I presume you either have a PIX or ASA since you are writing on these forums