[BoredGuy]

I think it'd be cool if you don't actually see Winter Soldier in this movie, but he's just hidden in every frame somewhere.
Like steve walks past bucky with a hood on the street, then you see a figure standing on a rooftop (almost imperceptibly) far behind cap in another scene, then a shadow whips past the camera in another.
Have him be almost constantly in the movie, but you don't really see him unless someone points it out