Turn a point and shoot to a waist level camera.
Interesting DIY idea, including the use of the PowerShot N that is currently dirt cheap to do that (~130USD$ on B&H) that seem to have been meant to be used like that.
As for the usefulness, I can tell that the way you hold your camera will change the way you see through it – this is why I have totally different results when using my TLR. This is almost like freestyle shooting. And it might bring in question from people – I have had people asking about my TLR when shooting – kind of a conversation starter.