Thanks for clarifying, 06gs430. There's actually a "nav kit" which will allow you to override the navi which is selling for $99. It's also removable as well, and bypasses the "I Agree" disclaimer. Although this is for the Prius navi system, it should work on the GS as well since it's the same unit. I'm not 100% sure, but here's the link in case anyone is interested.
http://www.coastaletech.com/nav_kit.htm