First of all, I want to say that your job doesn't look at all Photoshopped. Yes, it's not perfect, but will anyone notice? Not a bit.
Secondly, I want to say that you were looking at exactly the right method.
But because it's the opposite (black background not white) you have to make the background around the hair perfectly black, then use "Screen" blend mode (as opposed to "Multiply" in the white method).