He has a hukou ben and a Chinese ID, no? He is a fully documented Chinese citizen. Yes, he can get a notarial birth certificate.
Go to the gongzheng chu, where they said "bring us some documents and we'll notarize them," and have them notarize the documents in the form of a white book, or 出生公证书. The notation on the notarial birth certificate is 出生公证书, or chu sheng gong zheng shu, which is what you need to ask for at the Gong Zheng Chu, or 公证处֤֤֤.
Chinese documentation for use overseas is issued to Chinese standards. The consulate is WELL AWARE of this.