Easiest thing of all with a tesco visa are the online betting sites, surely? Credit your online account at skybet with 500 quid, then when you do a refund back to the card it appears (at least on my card) as a normal payment to the account, not as a refund of the original transaction.

The other thing I wondered is what happens if you Load £200 onto an amex TCC using (say) a visa debit/switch/connect card, then reload it with another £2500 using tesco visa. Spend some of it at any retailer that accepts amex, then get amex to refund the outstanding credit back to your credit card. How do amex determine which card to refund the money to? If they refund it to the original debit card then the money is conveniently in your bank account ready to pay your tesco visa bill
^