you've gotten some great responses so far. i may use them myself! having gone to PT, they gave me some exercises to do for this at home. you can certainly do them with a therapist if that's how you keep yourself accountable but they are things you can do at home. the hardest part for me was realizing that i was using the wrong muscles to complete the exercises, so in that case, a few visits with the therapist helped me immensely. i guess it all depends how in tune you are with your body.
here are exercises very similar to what they gave me: http://www.best-abs-exercises.com/stomach-vacuum.html
i haven't healed mine completely but it has closed some because, as with any exercise, you have to actually do it :P