Send the first Space Egg down into the pile of pebbles so they shoot up and come to a rest above the pigs structure. Repeat this with a second Space Egg in the another pile of pebbles. Assuming that you have a nice row of pebbles above the pigs structure, send another Space Egg and detonate it directly above them. This should send the pebblesrs into the pigs structure, taking them out. if you lucky enough, it's the pebbles can detonate the TNT to get more some points.