Yes, this is what I fear it will be like. I will try and give it a go with Trailfinders in London. I'm sure they are capable of dealing with a ticket that doesn't originate in the UK. China Southern definitely have got some interesting prices and routings (for segment runners) and it must be possible to combine the right fare classes to come up with a workable itinerary.

One routing actually passed through Xiamen after transiting Peking, with the connection to Hong Kong on Xiamen Airlines. Now, that would be an interesting one to try!