Transferred via GZ several times. There are officers at the entrance into the customers and they do check carry-on luggages from time to time. Many times they are there to check those black guys (go to the toilet to see what they are carrying), but occasionally chinese guys too.
So it is all depending on your luck and strategy. As long as you are checked, there is no way you can get these onboard unless you know someone up the hierarchy. There are pretty many chances that you can slip in without being caught.
My advice: can try, but better have plan B (get a friend to see you thru).