If you do decide to go for the 60-day membership, be aware that the only WC in SFO (and therefore the only location in SFO where a membership can be purchased) is in the international terminal.

Another way is to call up WorldClubs Service Center, purchase the temp membership over the phone, and have them email/fax you a letter of introduction/entrance (as it can take some time for the actual temp (paper) membership card to reach you overseas).