If you have to ship your phone back to the US, then you will need to ship is to a friend or a relative who actually lives out there. You CANNOT ship it directly to Apple as they will not accept it. Send it to a relative or friend that you have there and if you don't have any, then you are out of luck as there is nothing that you can do.
That is why is was not really a good idea to purchase an iPhone is the US when you are ultimately going to use it in China. With no international warranty on the iPhone you are stuffed really. You should have bought it in China and then you would not be facing this problem.
Nothing you can do except get on a plane and fly to the US or send the phone to a friend or relative.