You know what a barbell pullover is? Well do that movement on a cable column.
Basically take a straight bar and put it above your head on a cable column. Set the weight at reasonably low weight. Now, take the bar, put your hands on it about shoulder width. Pulldown without bending your elbows. Bend your knees.
http://www.exrx.net/WeightExercises/PectoralSternal/DBPullover.html
Movement should look like that with a barbell attachment on the cable. Put enough weight on so they are challenging. They made my outer back sore for several times.