Just take the email receipt people, set one up just for e-receipts. I get a rush and I'm not sorry either now when people come in with no paper receipt asking for an exchange or the money to be put on a gift card.
Me 'Ah you've lost your receipt? If you can just show me the e-mail receipt then we can refund you the way you paid"
Customer "I don't have an e-receipt"
Me "Oh dear, sorry there's nothing we can do then"
Customer "But, what, wait, waah, waah, waah. It's not fair"
Me "This is why we advise all customers to get an e-receipt, bye"
Also me "Who's next please, sorry to have kept you waiting. Would you like an e-receipt? Oh you would because you just saw what happened to the last customer..."