Massachusetts costcos are required to allow liquor sales to the general public, you just walk in through the exit door, past the membership/cust service desks, and you hit the food court before the liquor area. They only check memberships cards at the entrance door.

I don’t remember if they make you scan your membership card at the food court or not; if not, I imagine than that’s also available to non-members.

At least for the ones near me you just tell them youre getting food and they let you in through the exit.