Nightmare....the air ducts do have flexible pipes going to them behind the dash and it depends on just how accessible they are.....the ring will be sitting at the lowest point though and if you can unclip the carpet undertray below the steering wheel / glovebox area and tap the trunking you may be able to tell whereabouts the ring is sitting. On some cars access isn't too bad - on others its nigh on impossible. Good luck with it!
John
March 2008