I don't think being lean is the only thing needed. I've gotten really lean twice now(for two shows) and my abs have sucked because I've never really trained them very hard. For the last week and a half I've been training them almost daily using cable crunches and I've noticed a huge difference already. I say that you should train them with weight. HUGE weight. Today I'll be doing cable crunches with 210 pounds for 25-15 reps per set(I have no endurance so the reps shrink with each set). I don't know if it'll work for everyone, though I don't see why not, but it works for me. Give it a try.
By the way, I know I said to use "HUGE weight" and I realize that 210 isn't huge but my goal is to get the weight up to over 300.