Here's an excerpt I ran across on Bodybuilding.com. This may give you some ideas.
Method One - "Less Is More!"
One common method to training traps, is technically a method for NOT training them! With the "less is more" method, it is assumed that exercises like lateral raises, deadlifts, and military presses stimulate the traps enough to achieve full development.
This seems very extreme to some people, but if you have been training your traps with minimal gains on them for a long time now, you might want to look into this method for a month or two.
Completely dropping traps from the routine is hard for most people because they think they MUST shrug to improve their traps. This method is worth trying if you haven't gotten what you want from other routines.
Method Two - "High Rep Trap Training"
Another thought about trap training is that they are one muscle that tends to respond to a higher rep range. I've heard accounts where guys start to see explosive new trap growth from just changing the rep range to 12-15 reps per set!
You would probably have to lighten weights significantly for this, but your new development may surprise you. With this method to training the trapezius, you should take quality over quantity.
Focus on flexing your traps at the top of each movement! Just like any other new training method, I would recommend giving this a shot only if the traps are a very weak visual point on the body.
Method Three - "Power Training"
The third method to training traps that can be incorporated is "power training". This method is just what it sounds like- you focus on explosive compound movements, and heavy weights, but low reps.
With this method, you should work with exercises such as hang cleans and power shrugs. This is because in these two exercises, you can use an appreciable amount of weight to fully overload the muscle, and it they work well in low rep ranges.
This explosive training method is not going to injure you if you can perform the exercises properly, so I suggest working on form.