Often tricep exercises which are performed over the head put added stress on the long head. One good example is overhead tricep dumbell extensions. See the attached video.
Another great exercise is called a close grip bench. This exercise places the emphasis on the triceps instead of the pecs. Similar to a bench press, you do this exercise with your hands close together on the bar (Barbell). Also doing decline french curls are helpful in targeting that area. Lay supine on back with ez-curl bar (pronated grip- palm positioned so it faces you) raised above you with arms fully extended. Lower the bar by bending the elbow. As the bar nears the head move the elbows slightly back just enough to allow the bar to clear around the curvature of the head. Extend the arm. As the bar clears the head reposition the elbows to its former position until the arm is fully extended. Hope this helps!