i'm not a scripter nor can i present you any scripting solution from elsewhere but after i had read your request i thought to myself "why is he not just registering at one of the many dns forwarding websites like
http://www.no-ip.org
basic ip / dns forwarding is free and there are lots of free clients to download which you run locally to have your ip / dns automatically updated.
what you would have to do is to register an account and set up two dns forwards then make each dns point to your two different ips, install the clients and run via scheduler. :banana: