"Your itinerary is about a straight forward as it gets."
No it's not. He has a return ticket London/Shanghai on BA, and he has a separate return Shanghai/HKG on China Eastern. Nesting a ticket like that is not as "straight forward as it gets."
Like I said, he has to accept there is a risk that that itinerary will raise eyebrows at check-in and he'll have to deal with the check-in clerk. As the few posts in the sticky demonstrate, being right is not a guaranty you'll be getting on the plane.
The qualification 'about as' was having moondog's example in mind... you could have everthing on one ticket to make it slightly easier for the check-in agent to see when they initially bring up the booking. But that's about it.
I can't recall any reported incidents of this type of itinerary or ticketing being refused boarding because of TWOV eligibility, or subsequent refusal of TWOV plus entry permit on arrival in China. None of the posts in the wiki address this scenario because there are no reported issues (not just here on FT but other sources as well).