How about franked or branded ebook content? There is another word for it, but for the life of me I can't remember it. Basically have the owner's information included in the encrypted content so that it displays in key places throughout the book. Then allow the owner to download a fixed, but significant, number of copies over their lifetime in whichever ebook format is supported at that time. This does curtail the resale market a bit, but allows for loaning books to friends.
And it future-proofs things a bit, so that, unlike me, you don't have to keep your Gemstar reader around to read your Gemstar content.
