I used the Challenge Level from Chapter 3 (unlocked by getting Gold on levels 3-1 through 3-5). Start with a low power shot and head downwards. Try to stay as close as you can to each of the towers as you pass them, and don't forget you can also get Daredevil Icons by flying close to the ground too. Even after you've passed every tower, you can still get a couple more icons just by flying up and diving down to the ground. This is very tricky to achieve, but with a bit of practise, it's totally possible.