If I owned a restaurant, I'd add a QR code on the bill. It would be an optional feature.

The implementation wouldn't be too difficult. A programmer could make this in one day.
Waiters could be taught how to deal with it in one hour.
Risk of cheating would be so low that zero confirmations would be needed (status pending sufficient).
What would be printed on the bill would be something like this:

Optional:
Pay with BITCOIN.
$21.12 USD   = BTC0.04189 XBT
[QR Code]
Scan and pay with your smartphone.
Ask waiter for further instructions.