Back then, the trick was to get a generic Vanilla Visa or other prepaid credit card. A recent legal ruling meant they had to be run as a debit card for... reasons... I forget them.
But a lot of grocery stores would sell you a money order up to 500 bucks for under a dollar with a debit card (not a credit card).
So you'd call up the issuer and have them issue it a PIN. Then you'd run it as a debit card and buy a 500 dollar money order.
Subtract ~$5 for the GC and ~$1 for the MO and you could manufacter about 500 bucks in spend. And the best part? You could take that money order to your bank, deposit it, get the funds immediately, pay off your balance, then rebuy.
In one afternoon I earned enough points for a first class flight to a fancy European city, and eternal side eye from the grocery store clerks who were convinced I was up to something put couldn't put their finger on what.