"I don't know what you want to hear, boy. You want me to solve a problem but tie my hands when I try to help. You know I'm bound to report to the Ministry the fact that you are an unsupported minor, and if you don't have someone to take you in, they'll place you into foster care or a group home. It's unfortunate, and I'm sorry to tell you this, but at least it will not cause your education to cease."

So basically... you can't untell the Headmaster, much as he wished it.