Script not function if mouse is on object

I have modified the mouse orbit script from standard assets to function when the left mouse button is down, but how do I make it function only if the mouse is NOT over a certain object in my scene? Here is the modified code:

 var target : Transform;
 var distance = 10.0;
 
 var xSpeed = 250.0;
 var ySpeed = 120.0;
 
 var yMinLimit = -20;
 var yMaxLimit = 80;
 
 private var x = 0.0;
 private var y = 0.0;
 
 @script AddComponentMenu("Camera-Control/Mouse Orbit")
 
 function Start () {
     var angles = transform.eulerAngles;
     x = angles.y;
     y = angles.x;
 
     // Make the rigid body not change rotation
        if (rigidbody)
         rigidbody.freezeRotation = true;
 }
 
 function LateUpdate () {
 if(Input.GetKey(KeyCode.Mouse0)){
     if (target) {
         x += Input.GetAxis("Mouse X") * xSpeed * 0.02;
         y -= Input.GetAxis("Mouse Y") * ySpeed * 0.02;
          
          y = ClampAngle(y, yMinLimit, yMaxLimit);
                 
         var rotation = Quaternion.Euler(y, x, 0);
         var position = rotation * Vector3(0.0, 0.0, -distance) + target.position;
         
         transform.rotation = rotation;
         transform.position = position;
     }
 }
 }
 
 static function ClampAngle (angle : float, min : float, max : float) {
     if (angle < -360)
         angle += 360;
     if (angle > 360)
         angle -= 360;
     return Mathf.Clamp (angle, min, max);
 }