I also suffer from trichtillomania, only it's on my legs.

The only things I can suggest are distraction and relaxation techniques. If you find it's when you're in a certain situation, then perhaps you need to raise your awareness and think about what causes you to do it then. Then take yourself out of the situation for a short time. Things like relaxation cd's or breathing techniques may reduce the build up of tension that makes you pull (if it's the same as it is for me- the tension). I've always been too scared to bring this up at therapy, but they should be able to help surely, as it's like another type of OCD.