This has been popping up with quite a bit of popularity. First off, this forum has had a few threads concerning younger pine stock, so search those out. Second, brent at evergreen gardenworks has a few articles on training pines from seedlings to older stock. He covers the principles very well--guy has been doing it forever. Next, Jonas at bonsai tonight(blog) has quite a few posts on the topic. All those resources should give you a considerable bit of knowledge.