The Costco Visa doesn’t differentiate between membership levels. It’s also not the best card for use outside of some categories (gas, travel, restaurants OK). Depending on your annual credit card spend, it may not even be the best card to use at Costco. See this thread.
Even if you could do that directly (and you probably can’t), it’ll still be a withdrawal subject to income tax. I like Corndogg’s suggestion – use your already-taxed money for living expenses until your wife retires.
So in a year and a half your SSI will cover most of your living expenses. I don’t think your wife needs to work anymore. You both could have probably retired 5 years ago.