Oof. If he truly isn't aware of it, that's tricky. But maybe now that you've mentioned it, he'll notice. When my son was using too many wipes, I made a rule that after 2, the rest had to go in a little trashcan I put next to the toilet. He stopped over-using the wipes nearly right away. He has basically never used the trashcan; I think just remembering the rule was enough to help him stop at an appropriate point.
So I don't know if this would help, but perhaps if he had directions about what to do with the hair after pulling it out, that could help break the rhythm of the activity and draw his attention to what he's doing.