Disable specific settings dynamically

I am developing an iPhone app which uses Settings.bundle to let the user choose some options.

I have two questions regarding this:

1. How can I completely remove/hide some setting? (for instance if the app is running on iPhone 3G I want to hide settings regarding t开发者_如何学Che compass)
2. How can I disable (fade) a setting? (for instance, I have two Toggle Switches and if the first is set to OFF the second one has no meaning and should be disabled)

You can't. Your app cannot dynamically influence what is shown in the Settings app.