Migrating servers, domain/IP issue

[patracy]

I'm in the middle of migrating our vBulletin based site to another server. Our old server is still up and running. DNS is still configured to this IP address for our domain. I plan on leaving this in place until we're 100% on the new server. In the mean time, I was hoping to use just the new server's IP address to test the site. This works for the index page, but any login redirects to the old server due to the domain and vBulletin's settings. I've set my host file to redirect the forum domain to the new server's IP address. But every time I try logging in that way, I get a invalid redirect URL with the new server's IP listed in it. I'm assuming I need to update the settings under the admincp. But unfortunately, I can't log into it. Is there any other means I can get around this? I still have a lot of smaller issues to resolve so I don't want to change the DNS to the new server yet.