In the first scene with The Empire, Vader walks up to Piett and Ozzel. As he walks by, the camera zooms down on the pits below, where crew men look up at Vader in fear as he passes them.
One of them is an officer, the problem is that he is wearing the wrong rank insignia. 3 red squares, with 3 blue squares under and only one rank cylinder: that is the badge of a navy captain. The problem is that Piett was the captain of the Executor at this time.
Apparantly, decipher names a him a Lt. Commander, which presents a solution: Just give him two additional cylinders (those pen shaped things in their pockets), one at the right and one at the left. He's only on screen for like a couple of seconds, so hopefully it won't be too hard to do.