A familiar for any class

[Just Pete]

I've been running my gamers through the Legacy of Fire adventure path, and one of the characters has acquired Spooky as a familiar. Unfortunately, the character is a Cleric, and I have so far been unable to find a method to add Spooky to his portfolio.

I have been able to create Spooky, and to give him as a familiar to a qualifying character (wizard, arcane bloodline sorceror, eldritch heritage feat, etc), but have been completely unable to get it to work with any other class.

I can see from several places that the familiar button is called by the thing cArcFStart, and I'm reasonably certain that there is something in that thing that restricts it to a qualifying class - but I can't find that thing anywhere, or figure out how to add a tag that qualifies the character regardless of class.

Any help?