CX does not sell passes to their lounges, so buying it is out. You can try to get CX to comp you, as suggested, but I would imagine that they have hundreds of charity workers pass through HKG airport every day, on their way to various assignments. You can also try to find someone who will invite you into the CX lounge as their guest (a popular FT activity). There are paid lounges at HKG (not affiliated with any airline) but these are not very good, certainly nothing like the Wing or the Pier.