It would be very difficult, because it will have to be a certified "acceptance agent" by the National Passport Services office, and doubt anyone has that in China.
Anyway, in order to add pages to your current passport, it needs to have only a maximum of 4 empty "visa pages". If more, no dice.
You must make an appointment with the Embassy or Consulate on line, and on the date and time show up with your passport, application form (download from internet) and money to pay fee.
The fee for this service within USA is $ 82 for the extra pages, $ 60 for expediting and $ 12.50 for delivery last time I did it there. At Consulates and Embassies the fee is higher; I heard Guangzhou charges $ 125, but I have not confirm this myself.
An almost unkown fact is that you can request either 24 or 48 extra pages for the same fee by regulations. If you do not say one thing, you get 24, and you can only add pages to your passport once, even if you only get 24. Next time you must get a new passport even if not expired.
Hope I have helped you some. Good luck !

Thanks for info.  Was aware of what you mention.  Only have  page left, and pp expires in two years anyways.  best choice get new passport and request the max pages,48 at that time.  was wishfully hoping to avoid a trip to embassy.