The apache manual says:
Serving the same content on different IP addresses (such as an internal and external address).
The server machine has two IP addresses (192.168.1.1 and 172.20.30.40). The machine is sitting between an internal (intranet) network and an external (internet) network. Outside of the network, the name server.example.com resolves to the external address (172.20.30.40), but inside the network, that same name resolves to the internal address (192.168.1.1).
The server can be made to respond to internal and external requests with the same content, with just one VirtualHost section.
Server configuration
NameVirtualHost 192.168.1.1
NameVirtualHost 172.20.30.40
<VirtualHost 192.168.1.1 172.20.30.40>
DocumentRoot /www/server1
ServerName server.example.com
ServerAlias server
</VirtualHost>
Now requests from both networks will be served from the same VirtualHost.
I know this is specific configuration, for internal and external network, but I think i can be run for two external IP's.