Quick way to make the output .lrs compilable with lrs2lrf:
1) in the <BookInfo> section, remove all readings, e.g.:
<Title reading="">Winning (Excerpt)</Title>
2) for <BookID> tag, make first two characters read "FB", e.g.:
3) compile away!
P.S. I didn't try it with all books. Let me know if you run into any issues.