I imagine something like this. Just a quick sketch. (I now remember how out of practice I am.)
I gave him most of the Vader armor but with a cloth collar like Ben's in ANH. Or maybe a pilot scarf thing. Originally I was going to have him in an ROTJ Luke-type outfit - that would work well too. Or something like this:
Maybe he only wears what I drew after he starts to support the Emperor's New Order.