You may not have enough time

to get all the paper work done. Once you get the J1 waver reciept form the State Dept. Your may not change or extend your status. Is the maximum J1 status 3 years? If it is, you are stuck until your waiver is approved. But think positively when you have to go back to China. I went back for my H1 and had nice time with my family and friends.