Dear Benjy,
I have heard that it is very hard to get information on homebirths in HK. They do happen, but often they are accidental and not the planned variety. You might want to start by calling some midwives in HK such as Everdawn 9417-6366 (Mrs. Chee) or Annerley Midwives 2983-1558 (Hulda). They would be likely to share any info they have with you. While it is true that the system does not support homebirths here, there may be legal ways of doing it. In Singapore where it was thought to be technically illegal, several of my friends researched it and discovered that if they had a certified midwife attending, as well as a registered Dr. overseeing, then it was ok. Perhaps the same is true here? Many people there flew in a midwife from Australia, UK, USA for the delivery.
Do share whatever you dig up, if you don't mind - I'd love to have the facts.
Best of luck to you!