What would be the point of using a Perfect Defense in this case? They can willingly and freely decide not to commit to the attack, which would result in the shaping effect not happening, so why would they spend motes, willpower, or anything else in this endeavor if they can just stop the attack? Again, they are effectively being provided with a perfect defense here, which is just not committing to the attack at the cost of not having their attack connect.
Another way to look at it is that the bypassing is part of what makes this Charm a Perfect Defense - normally inflicting an Derangement on someone is an attack, but in this case it's a defense. A strange defense, but still a defense. Since it's a Perfect Defense, the effect works no matter what.
Because they are Perfect Defenses, messing with those is bad juju as stated by others before me.
Just have it do something else appropriate to Oramus if the opponent has a shaping defense or refund the motes into an overdrive pool.