1. Use a slight lower back action with help from the calves to create momentum and get the bar moving.
2. Quickly shrug your shoulders up as hard as you can. Try to hold the top position for a one or two seconds to increase the time under load.

You can use power shrugs as a stand-alone movement. Do 5-8 reps. Or do them at the end of a set of regular barbell shrugs: perform 6-8 heavy strict shrugs followed by 4-6 power shrugs once fatigue prevents you from doing the strict movement. You'll actually get some core and calf work too.