Idea!
While he is young, Naruto stumbles upon a crater in the woods, a crater with a hammer in it. Curious, he tries to pick up the hammer. He cannot lift it. But in his ear, he hears the whispered words, "Whomsoever holds this hammer, should he be worthy, shall have the power of Thor." So Naruto asks, "What does it mean to be worthy?" The whispered voice answers. And so, Naruto embarks on a quest to become worthy in the eye of Odin, Lord of the Aesir. That's right, Naruto has just imprinted on Thor!