As far as I know, You can't do that. The home button functionality is not accessible via any event handlers in Objective C.
You only get "notified" by the UIApplicationDelegate whenever the app is resigned from being active or becomes active, but you can't display any alerts there since you can't lock the home button or make the user wait for an alert for the home button to work.
In summation, The home button must always go home, It doesn't matter what your application wants or needs :)