How can I move focus between OverlayItems on a MapView using the d-pad?

I have a MapView with an ItemizedOverlay containing a number of Ove开发者_StackOverflowrlayItems.

How can I let the users to switch the focus between these OverlayItems using the d-pad or cursor keys? At the moment the MapView never even gets focus, the highlight just moves between the action bar icons and the zoom buttons.

If this is possible, would the user still be able to switch between scrolling the map and moving between OverlayItems? Possibly, the map could just be made to scroll as you move the focus to an item off the screen so the item is moved into view.

I'm doing this to try to remove the requirement for a touchscreen from my app. This will improve it's accessibility and allow it to be used on Google TV.