Ok time to clean up the shop. I have a home engineered backrest/armrest combo that bolts to the two bolt holes on the factory backrest bracket. $40 + postage, this is a great thing for the wife or kids who like a little extra security on the back seat, and its easily removable.
Also have a large JCW trunk with custom made mounting bracket that bolts to the same two holes in the stock backrest bracket and the rfear tail sub frame. $65 + postage. This bracket is way stronger than anything anyone sells. Comes with two keys.
PM me if interested.   

Jim I am interested in the arm rest. Well let me rephrase that, I have absolutely no interest in it; but my wife would LOVE it
Guess I forgot ask, can this be mounted without the backrest pad?  I have the backrest extension that I designed and made. The SO has become quite fond of it.

Jim I am interested in the arm rest. Well let me rephrase that, I have absolutely no interest in it; but my wife would LOVE it
Guess I forgot ask, can this be mounted without the backrest pad?  I have the backrest extension that I designed and made. The SO has become quite fond of it.

Yes the backrest pad can be removed and the bracket cut off, then it would bolt right on behind your extension.

Armrests are sold, trunk still available.