I had the almost same case as you, 中国大使馆要求固定套, at that time, what they ask was one round hole固定the whole set of documents, I shop around and even ask my lawyer, no one know where can find it, end up I back to 中国大使馆 and told them I can't found it, then the lady just did it for me right the way, can't believe why they didn't offer help at the first time. Hope they can help you too.