Hmm. I've never had the need. Let's see. What if you put some whitespace in between <mbp

agebreak />'s (e.g., or <br/>, or some white graphic; or or some white innocuous text). Better yet, you could put some decorative graphic or illustration so that readers wouldn't think that the book is broken or misformatted (that's what I would think if I saw a blank page).