http://askthetrainer.com/oblique-exercises.html

If you have straight bar with attachments on each end such that the one which comes with the life fitness Dual Adjustable Pulley you can perform high cable wood chops.
This is a great exercise for your obliques and core. Anyone involved in an activity which has movement in the transverse plane such as baseball, tennis, hockey and any throwing sport can benefit from this core obliques strengthening exercise.
Set the cable pulley on its highest setting. Grip the bar with an alternating grip with your hands placed on each end of the bar. If your are chopping to the right your left hand should be at the top of the bar with your palm facing upwards and your right hand should be on the bottom with your palm facing down.
Assume an athletic stance with slightly bent knees and step a couple feet away from the machine so the weight stack will not touch for the duration of the movement.
Draw in your core and chop diagonally across your body. Your upper hand should bear most of the force with your lower hand serving more as a guide as you rotate the bar inline with your belly button. (less info)