I believe that cutting the fat AND the water is what makes them show. I don't know of anything that specifically develops them. Part of my pre-contest routine is to do this (seems to help bring out the serratus): Use a high pulley cable machine (experiment with amount of weight but start light!). I use about a 2-foot long, heavy piece of rope with knots on the ends. Use an attachment (I use a LARGE snap-lock that I get from a saddle shop) to attach rope to cable - so it moves freely. Grab rope and get on your knees. Pull down, schrunching somewhat, going from right to left, then vice-versa (bring your right elbow down to your left knee - or past it, then do other elbow). Do 5-8 reps per side (10-16 total reps).
Can you make any heads or tails out of this description?
xcel