Put the roller all the way up and all the way forward on the GHR hook your feet under the bottom roller and you have a decline sit-up machine. Lay back until your torso is in a decline position. Keep the tension on the muscles in your stomach to keep pressure off of your back. On the way up push out in your stomach like you are squatting.
Shoot for 100 total reps on this. You may have to build up to that though.