Harry was silent as he considered, Draco hadn't asked why and he figured the Slytherin understood the need for discretion. He hoped that Blaise would too. And Ginny trusted him.
"Okay." Harry said simply, "we can tell him it's a charade."
"Do I only have three weeks to learn French? Or is there a charm for that?"
That was his biggest concern to pulling the disguise off. He was getting good at changing his physical appearance.