I don't have bdd, but I can relate to what you are saying and going through. A psychologist told me one time to do what you fear - a lot. For example I feared wearing running tights and triathlon clothes. I broke out of the fear by over exposure, I wore them even though I was petrified, for several hours during events. It really helped, but it was so hard to do initially. I can now walk in a swimsuit without a towel covering me and its not that big of a deal.
Maybe you could try bits or chunks of exposure. Like either make yourself go out without make up grocery shopping (avoiding mirrors and such) and keep doing it even though it is really hard. And don't look in the mirror before you leave, just go.

What have you tried do far? One thing I know for sure is to avoid mirrors and reflective things as much as you can? How often are you using them?