Modify "Humanoid" Animations

I've created my arms with FPS mesh tool Look at the hierarchy, there's still the normal body bones. I also created a IKArms script to handle correctly my weapon sway effect (love it)

 #pragma strict
 
 var animator : Animator;
 var ikActive : boolean;
 var rightHand : Transform;
 var leftHand : Transform;
 var rightHandTarget : Transform;
 var leftHandTarget : Transform;
 var lookTarget : Transform;
 /*
 var bodyPositionOffset : Vector3;
 */
 function OnAnimatorIK () {
     //if the IK is active, set the position and rotation directly to the goal. 
     if(ikActive) {
 
         // Set the look target position, if one has been assigned
         if(rightHandTarget != null) {
             animator.SetLookAtWeight(1);
             animator.SetLookAtPosition(lookTarget.position);
         }    
         // Set the hands target position and rotation, if one has been assigned
         animator.SetIKPositionWeight(AvatarIKGoal.RightHand,1);
         animator.SetIKRotationWeight(AvatarIKGoal.RightHand,1);
         animator.SetIKPositionWeight(AvatarIKGoal.LeftHand,1);
         animator.SetIKRotationWeight(AvatarIKGoal.LeftHand,1);
         animator.SetIKPosition(AvatarIKGoal.RightHand,rightHandTarget.position);
         animator.SetIKRotation(AvatarIKGoal.RightHand,rightHandTarget.rotation);
         animator.SetIKPosition(AvatarIKGoal.LeftHand,leftHandTarget.position);
         animator.SetIKRotation(AvatarIKGoal.LeftHand,leftHandTarget.rotation);
     }else{//if the IK is not active, set the position and rotation of the hands and head back to the original position
         animator.SetIKPositionWeight(AvatarIKGoal.RightHand,0);
         animator.SetIKRotationWeight(AvatarIKGoal.RightHand,0); 
         animator.SetIKPositionWeight(AvatarIKGoal.LeftHand,0);
         animator.SetIKRotationWeight(AvatarIKGoal.LeftHand,0); 
         animator.SetLookAtWeight(0);
     }
     //animator.bodyPosition = animator.bodyPosition + bodyPositionOffset;
 }

Simple. The Arms animator does NOT containt ANY animations, because IK does the job very nicely, and i can't create animations with humanoïd things. (sadly...) The IK in action : How can i modify my animations arms without any external program? :)