Sorry, there's no way to do this currently. There are a couple of global settings for indentation on the Book Theme page that I'm sure you already know about, but there is no per-paragraph way to do this.

You can find the Book Theme page for your book here:

leanpub.com/YOUR_BOOK/theme

...making sure to replace "YOUR_BOOK" with your book's unique slug.

Did this answer your question?