If the time spent in HKG between scheduled arrival time and scheduled departure time is more than 12 hours, then bags cannot be through checked. CX won't even bend that one when arrival and departure is on CX. Apparently its a HKIA rule.

If less than 12 hours in transit then you may have a chance.

There is left-luggage facilities at HKIA in the arrivals area after you exit from customs. As you exit, turn right and its well signed at the end of the hall.