Here’s a cheap trick. Create your book on Amazon and/or Smashwords.
On Amazon, at the end of the first screen of work, you’ll have submitted your ms and Amazon will “crunch” it and produce a “preview” for you to review.
In the “Downloadable Preview” box, click on “Download Book Preview File”. You’ll get a mobi copy of the converted book which you can save on your computer and send to reviewers. You can get this file even after you’ve published the book.
Then click on “Save as Draft” if you’re not ready to publish. It’ll be there when you come back. Be careful to do this if you intend to do a “pre-release” sale. If you publish your book, even by accident and then “un-publish” it, you won’t be able to do the pre-release sale.
On Smashwords, you’ll have to completely publish the book, then go to the sales page and download each format you want to use. THEN “unpublish” the book until you’re ready for the official “coming out”. I don’t know what problems this can create for a pre-release sale there.