Equip either the Invincibility power-up or the Fire Suit. It is best to equip some Speed-Ups, Bomb-Ups, and Flame-Ups for the trick to be more effective. Plant a bomb and stand next to it, waiting for it to explode. Meanwhile, repeatedly tap A to plant a second bomb in the blast, then another, and so on. The process can continue for as long as desired. Having the Bomb-Ups simply means the chance of failure is reduced, while the Flame-Ups and speed-Ups allow you to cover more ground during the time you are invincible to the bomb blasts.