There is another easy way to spend Visa/MC on Costco, if that is what you want to do.

Go online and buy Amex GC using your Visa/MC and spend that in Costco. They even give you 'Cash Back'. Use 'Cash Back' to deplete the whole Amex GC, so there will be no balance left.

Buying the Amex GC, you will meet your spending threshold plus points. Also if you buy thru referal, there is a 1.6% cash back (IIRC).