have asked. not possible... (5000 for HKG-TPE-HKG on new years eve)
but I believe (and have heard) that if you find *consolidated ticket* agents, you might get some luck as they have to get rid of tickets that might have.
also, i wonder how often does CX have the number of empty seats that they have to throw away. often i only see few empty seats. there is no point to start such a *rule* for a seat or 2 so that people would actually start abusing them.