Only someone who has had a specific Agiel used to train\break them suffers the pain it brings while wielding it, and only while grasping it, physical contact alone isn't enough.

That's easy enough to do though.. while wielding it you suffer the consequences, and it only brings on the pain(damage) from attack rolls(touch attacks would be fairly accurate representation too)

You could do a whole slew of techniques from out right intense pain (highest damage) to continous damage(bleeding) to physical stat damage( like dex damage might represent breaking ribs or something) upto save or die(stop heart)