Well, if you want a quick (and maybe a bit dirty) solution, select the mesh of the character where you want the blazer to be, so basically his torso and arms, and then copy that mesh, now apply a push modifier to move it out a bit.
Of course you still have the shape of the character, so try the relax modifier to smoothen that out a bit, to finish off apply an edit poly modifier to add details and make fixes, finally you can add a shell modifier to add thickness.