Yes there is a app out there called oneClick, I started a thread about it a while ago. Will try tp find it for you. It puts a soft home button on your screen, and you can move it anywhere you want plus of course it is always on top of everything, so you can tab it.
Edit: Sorry it's called clickonce. Here is the thread and the app to download.
Soft Home Button for iPhone released
Isn't that not worth one thanks click?