You could try editing the HTML file of the book (Notepad ++ or KompoZer are my favourites).
It should look like
<p>paragraph</p>
<br>
<p>letter</p>
<br>
<p>paragraph</p>
Also working:
<p>paragraph</p>
<blockquote>letter</blockquote>
<p>paragraph</p>
Using blockquote, the letter indents and there's space before and after. In the lower part of the screen attached, you can see the quote, and a quote with <br> to simulate a verse