I am not a therapist. At all. And I have no experience specifically with excoriation. BUT.... If you haven't tried forming replacement habits yet, spend some time on it. When your hand starts moving towards your head, instead of stopping it, direct it to a 'safe spot' on your cheek, shoulder, neck -- anywhere where it will do less damage. I would recommend the hair behind your ear, as it gives you something to fidget with, but your needs may vary.

As a random thought, would something like this help? This may not be the best example, but various mechanical barriers are available, including things like this and beyond.