Twist answer- only have one camera!

Then, have two transforms which are managed separately- one on the scope, and one for the main character. Treat these transforms the same way you would use a camera in terms of movement etc., and then when you want to change camera, do this-

Camera.main.transform.parent = transformYouWantToChangeTo;
Camera.main.transform.localPosition = Vector3.zero;
Camera.main.transform.localRotation = Quaternion.identity;

use a lerp: http://unity3d.com/support/documentation/ScriptReference/Quaternion.Lerp.html

and assign the result quaternion to your camera