The only thing that really started to work for me, was doing more sets, and using a shrug machine with a 'side' grip, like using dumbells. If you dont have access to one of those, I find that heavy barbell shrugs work ok for me, but not quite as well. I am not that strong of a guy, and I'm tall, but for me my routine would be roughly 5 plates/side on the shrug machine, or 315-365 barbell shrugs. Traps are not my genetic strong point either, so I think its one of those things you have to learn to punish, and concentrate on for awhile.