You might try smith machine presses on a low incline with a super wide grip. I have been doing these the past few weeks and my outer pecs have been feeling the wrath!
try incorporating many different fly variations into your workout...incline, decline, DB, machine...etc.
well this is an old a$$ post but i was lookin for some stuff on chest width. the problem with me is i have this popping pain in my shoulder when i do flies. i may be able to get away with like a set if i warm up my shoulders for a long time but after that i'm done for. i had talked to a few people at my gym including trainers but nobody really knows. the best guess was a tendon rolling over a part of the shoulder or something like that. i most definitely need width in the chest though and all my chest lift i have a wide ass grip already cause i like it better. the only thing i can really do for flies is machines and we just have the seat straight up so it's hitting the same muscles that flat bench would. any help or suggestions?