It's all about a big back and small waist...that is what makes you look wide. Also don't overdevelop the traps in relation to the delts. I don't buy too much into the appearance of width being genetically determined...when I started lifting people said I had narrow clavicals and would never be wide, and now they say I have a naturally wide frame, so I don't buy into that whole line of thinking.
Also, have you ever noticed that the "frat boy lifters" who train chest 3 days a week and never do back all have slumped postures that make their shoulders look even narrower, especially from the back?