They say that if you make paper out of dried habaneros, bind together one hundred and eleven such pages, find an imp with nine ex-wives and have him fill the book with infernal obscenities and then eat the book. And survive. That survivor might indeed be granted +5 to constitution.
A +5 wis book may typically come into being when an old, wise monk or priest is Magic Jar-ed into a book. The host body is then slain and pickled in holy water. Later, the remains must be freeze-dried and mixed with ink. The ink must then be used to artistically decorate the cover of the book with quirky poetry.
The latest known +5 strength book, history tells us, was in fact an ordinary yellow-pages book. Sir Margareth the Bold used it as her last weapon of defense when her family castle was overrun by centaurs. Having been disarmed of her trusty longsword, she picked up the book and beat to death no less than fifteen centaurs before they managed to flee from the crazed knight gripping the blood-dripping volume. A servant, cleaning up the mess later on, picked up the book, flipped through it and suddenly qualified as squire!