Hmm. Something like, he's already just become a whitelighter and comes across Seph's attack? I'm thinking since he would be a whitelighter, the elders would naturally tell him about the existence of magic and demons and such. So he would see something and intervene? Is that what you're getting at? Sorry, it's almost 3:30am and it's been a long day! I'm pretty tired so I'm a little woo at the moment haha!
And yeah, I can see him watching over Petey. That'll work :)