If you don't have a Costco membership card, you can still buy alcohol at Costco for the same price the members pay. Costco can't offer "club" restrictions on alcohol.
You need to get a pass at the member services desk (it's actually a 1 day pass) that get's you in. You can only use it to buy alcohol. Costco can't charge you for the pass. You can get a pass any time you'd like as many times as you'd like.
Club's have been known to play "stupid" about the pass or the fact they have to let non-members in to buy booze. Eventually they have to give in.
