Adolf - it seems the quickest way to make some coin is by app design - so why not design a yonnie-piffing app, which relies on you holding the phone like the stone (ie; around edges) and as you do the motion, it relays your technique to the screen (with multiple scenes - pond, river, ocean etc.) and replays from a couple of different angles including a moving camera - I'd download that one for free...might even pay a couple of bucks for it!
...might want to start selling wristband attachments also re; initial issues with wii handsets & big-screen tvs!
[edit] sorry to burst your bubble - already an app out there 'stone skipping'!