Ermmm a good solution for some, but honestly...... just get the armrest replaced under warranty.
Having a extra pad stuck on like that looks rather awful

Perhaps get a custom armrest section made for a specialist?
Shouldnt be too difficult:-
order new armrest door car
de-cloth
add new foam
re-cloth and stitch
swap with existing one
When you come to sell the car you still have the original plus a modified version?
