i found a great way to work it but it is hard to explain but i will try.
this is at the end of the workout
i incline the bench more than usual by a peg or so. ( i usually do 25 degree incline, but i am talking about USUAL since most do 45 go a little more incline)
incline the seat up aswell to really sit you in there. now lay down on the bench and put your shoulders back and down, and i mean BAAAACCK and your sternum high as can be so your chin gets sucked in.
now with the DB bring them back until your arm naturally stops going back so they are pinned there. bring them wide and down and stretch stretch stretch . if you got it right you will feel right under your collarbone stretching then push up about 1/4 of the way up and back down, over and over....
awesome results for me and some others
but try it and see if you like it everyone is different