HKG is in Asia Zone 2.

As you know, stopovers less than 24 hours are allowed. You should be able to do a stopover in Asia 1 on your way to Asia 2.

Asia 1 is only Tokyo, Korea and Mongolia.

Your best bet would be a less than 24 hour stopover in Tokyo on AA or JAL metal continuing onto HKG on JAL or CX metal. For this routing, if possible, I would target HND instead of NRT as NRT is quite far from the city.