You might want to also try training the abs with weight to increase the size of the abdominal muscle, so it will show through more. If you already do this, you may just need to clean your diet up a bit, but otherwise, try doing some weighted crunches.
You can't seperate them any more than they already are. You can make them bigger which may give them deeper cuts, but without some sort of bizzare surgery, they are separated as much as they are and that's the way they'll stay.
Lose body fat, combined with building them up (so they "poke" through the existing fat a little bit more) is all you can do. Period.