As the function of the traps is not only to raise the shoulders but also to pull the shoulders back try using the low pulley to do shrugs. Make sure you face the pulley and stand a few feet away from the pulley so it pulls at an angle Figure out which handle or straps will work best for you. Straps will let you do this exercise more like holding dumbells and have your hands by your side . The low pulley is going to provide tension both down and forward as you do the shrug motion. REMEMBER to pull your shoulders back as well as up. So you have tension coming from 2 different directions unlike the barbell which provides you with only one direction when doing a normal shrug. Try it and develop the YOKE you want!
For those who want additional Trap stimulation, try doing bodyweight ring shrugs or inverted upright rows after you do the low pulley shrugs. For those who are not familiar with this, you will be hanging upside down holding onto the rings to do these. This will really finish off your traps!!
Heavy barbell and dumbell shrugs , along with deadlifts and power cleans have always been suggested to develop traps. Rows and overhead presses also work this area. But the exercises I suggested will work the traps very well if not BETTER than the usual way and an added benefit with much less strain on the spinal erectors which in most cases need more recovery from heavy squats and deadlifts.
One more point I need to mention is that traps will respond better to higher reps. The reason being the shrug is an extremely short range of motion and more time under tension is needed. So I would recommend no less than 20 reps . Once again , EXPERIMENT !