Hi,
The armrest can be retrofitted with or without your current centre console. If you dont mind the vents not working on the rear of the armrest, its easy enough to remove the back part (the big bottle holder section) and replace it with the armrest section. If you want the rear vents to work, you need to change the centre console as well as it is shaped to include the ducting from the front of the console along the floor to the back of the armrest. I dont know why your dealer is saying it cant be done, it is a couple of hours work but they should be able to do it no problem if you dont fancy tackling it yourself.
Cheers,
Dave