Inquisitor Warning ability?

[Xaryel Delmorsiege]

I have another question for the inquisitor in our group he has the archetype preacher (UM page 46) and likes to use the ability "warning" a lot. Our question is if an enemy hits an ally with a critical hit, can he use the warning on the conformation roll for the critical hit?!

[uriel222]

By RAW I don't think so, but as a GM I don't think it would be game-breaking to allow it. It would certainly be more cinematic to call out a warning about a potentially fatal blow than an incoming paper cut, anyway...