Technically and legally speaking, you need to present a Foreign Expert Certificate (FEC, now "blue book") when exchanging renminbi to foreign currency, not for wiring money.
However, as a practical matter, you don't really need the FEC to exchange money. Check the chapter in the Guide titled Currency and Banking
: You can use the gray market of money lenders for doing that (outside the main branch of the Bank of China), or you can ask any Chinese national to exchange the money for you. Depending on the city, branch, and mood of the teller at that particular moment in time, you may even be allowed to change renminbi into foreign currency without presenting the FEC.