Not sure about that Steve. I've always felt that when the traps are very well developed and high, it creates the illusion that your shoulders are actually narrower than they really are. So if you have width issues due to genetics then I'd actually stop trap work and concentrate on side delt work. A routine I've used to beef up my side delts involves some overload drop sets.
- one arm lateral rasies:
2 drop sets - heavy (target 4 reps) immediately grab a lighter DB and rep out to failure (target 8-10 reps) then grind out as many X reps as you can.
After completing the 2 rounds of drops, go for a regular set of lateral rasies (10-12 reps)
Your side delts should be toast by this time so really finish them off with 3-4 sets of behind neck presses on the Smith machine (trying to balance a regular BB at this stage of fatigue might be dangerous). Go for something like 10, 8, 6 & 6 with bottom position X reps. This is a great shoulder/side delt shocker. Give it a try!