Only way I've ever seen it done is by cutting off the outside fender at some appropriate cut lines (like the top crease and the door gap) leaving a 1/2 inch or so of the old fender skin behind for joining, and then splicing in a replacement piece cut from the donor car.
Since the X is a unibody, there are no bolts or tricks to get a fender off. Everything is welded, and the only way to get the outer fender skin off is by old fashioned cutting tools.
Somebody may have a better method, and if they do I will be glad to see it.