You can tell your friends about this e-book using facebook, you can post a link there. You can also use articles directory where you submite an article to be read by an audience already interested in your subject matter. Do not forget to post a backlink to your e-book in your article. I hope that helps.
I think you should take another approach, instead. The approach your already saying to me, would be your site is already established with traffic, and links built to support your niche. Its easier if you have an audience already to sell, then no one being there.. if that makes any sense.