Instead of waiting until hole four, you can actually get this on hole one in the Caribbean Cup. Immediately after starting the cup, switch to your 3-Iron. Turn on power hit by pressing B. Try to get the ball as close to the water as possible while staying on the striped green part. Go for the hole on your second shot, most likely using the 3-Iron again. Adjust your shot for wind and use the focus (slow-mo) to your advantage for an Eagle and achievement. It may take a few tries, but it should not be too difficult.