Just clone the magstripe on a friend's Costco card for the gas ;)
What I don't understand is why no gas station other than Costco has hoses that can reach around a vehicle.
Regular gas stations rarely have a line of people waiting for a pump. Costco often does. Managing that queue becomes much easier if any car in line can take any open gas pump, without worrying about which side the tank door is on (or messing with the flow of traffic by trying to back into a spot).
I can understand the rareness part, but some gas stations are known for being discounters, but I still haven't seen them use it, despite their traffic jams.
For the digital card to work for gas, Costco would have to install QR code scanners on gas pumps.
(My next-best card in terms of rebate on gas is 1.5%, so assuming an additional 2.5% from Costco, I need to buy $2400 in gas to have the full membership covered by just the gas rebate - not even counting the additional savings from the lower price of gas).
I guess it's somewhat expensive if you're buying it for this purpose alone, I'm sure you could find a cheaper used one on ebay.