I think I know what you guys are talking about, here's how it's done:
The hero ability which you learn is actually a modified " engineering upgrade " ability
The hero already has a normal (non-Hero) spellbook at the x=0, y=-11 position, but initially this spellbook is empty; it contains no passive abilities
There exists a second spellbook ability with all the necessary passives within it, its also supposed to be located at the x=0, y=-11 position in the abilities gui.
The Engineering upgrade ability is modified such that it replaces the empty spellbook with the spellbook full of abilities
Let me give you an example
Spellbook 1 abilities : none
Spellbook 2 abilities: permanent immolation, spell immunity, defensive bonus, attack bonus
Engineering upgrade renamed to "Might of Ifrit"
Description reads something like "Bestows upon the hero the intense powers of Ifrit, thereby giving him permanent immolation, making him immune to all spells and magic attacks, making his attacks stronger, and enhancing his defense"
In the abilities which engineering upgrade will upgrade, it should name spellbook 1 as the ability it replaces, and spellbook 2 as the replacement.
Anyway you guys get the general idea....this is a very useful tactic btw