Flipping around on some sites last night, I stumbled upon... Now, it doesn't work exactly as you would expect, but it's definitely an improvement for using the G1 with a single hand. I did not have anything to do with the development of this application. You can find the application's page here. You can download the .apk file here. Those of you like me that are curious about how it was done (source code,) here you go.