Idiom for global shortcuts on mobile devices

I have a mobile web app and there are two different modes for viewing content and the user may frequently toggle between them. I'd like to provide a very convenient way for the user to request this toggle action.

A link onscreen isn't good, because the content is full screen and so the link would block it. Gestures might be okay, but might also interfere with what each view wants to do with a gesture.

What I'd really like is the mobile equivalent of a global hotkey, something that you can do that would be handled by the app and then relayed to the content pane if not handled globally.

Is there a good way to accomplish this?