In a BTC-welcoming restaurant scenario, you are far more likely to receive your change as multiple BTC bills pre-printed by the restaurant in a small denomination conducive to leaving tips, with scratchoffs protecting the private key. Your restaurant receipt will list the firstbits of the change bills that were activated for you as proof that the bills were funded by the waiter before being brought to you.
Or they can make new private key for the change and print it on the receipt.
Then the waiter can steal it with a camera phone - that is the concern I was looking to address.