diastasis rectus abdominis

Has any of the veteran sleevers had diastasis rectus abdominis and have it corrected after loosing the weight? I recently found out that is the big lump that comes up when I try to do crunches etc., and that I shouldn't be doing them with the muscle seperation.

I have not always been obese, but always had to fight being overweight. I went from 240 to 300+ very fast, resulting in seperation of the rectus abdominis muscles. I understand women often get this during pregnancy. I was looking forward to getting my abs flat again, but have found that I have to correct the muscle seperation prior to doing the normal ab workouts. Anyone find anything that worked well correcting this?,, Many thanks!