This "preregister online" for TWOV s BS. There is no way to do this and certainly it doesn't happen for PEK/PVG/SHA. You do need to tell your airline at check-in that you will be doing TWOV but this fact usually comes out anyway when they inspect your passport for a Chinese visa and find none. The airline should transmit the actual passenger manifest to Chinese immigration (not sure when or by what method this is done) that has all the various visa, TWOV, or no-visa-required statuses for all passengers. Which is not under individual passenger control.