No, actually I was just Wondering and have NO intention to do it. Before CX introduced 3 flights to HKG from SYD it does not really fit in the Schedule (As I want a full day in HKG to do a few things before I get on the night flight to LHR - all within 24hrs).

Interesting that the checkin agents will police it? I thought they don't care as it only affects the issuing airline?
How would the checkin agent know (normally thye don't even ask for all of the tickets (and CX does not have access into BA/QF's reservation system?)