I don't think I-140 approval will block you to get H1B visa in Beijing ,because you ever got same one there,and never try to change status with INS.
If you want further safe,you may try apply visa in Mexico, as my experience ,the consular officers in Mexico ,usually have less prejudice to Chinese than
in China,and if you are checked , you may come back to your home in U.S.A to wait the result.
Just in case of denial ( I never heard ),you still may
go back to China ( via Euro tranfer without visa ) to apply again. Good luck.