My car originally came with rear headrests but I broke the rear parcel shelf and replaced it with one that didn't have the holes for the headrests, and I didn't mind the improved rear vision that came with that change.
But the rear headrests do look nice, so I thought I might refit them.
I believe that all coupes have the mounts for the headrests, you just need the headrests and either the correct parcel shelf or you can just drill four holes in your parcel shelf.
You will need four of the plastic trim pieces to cover the holes (P/N 52208135923 for black, but other colours available), and four spring clips (P/N 52101928809) to hold the headrests in place.
I opted to drill the holes in my replacement parcel shelf.
To drill the holes in the correct place I looked at pictures of the correct parcel shelf online to get an idea of how far back to drill, and then lined up with the mounting holes underneath.
I did the measuring and the drilling with the parcel shelf in place (and with a vacuum cleaner handy), partly to make it easier to line up the holes and also out of laziness. Otherwise, you have to take off the C pillar trims, and rear side trim panels too.
Surprisingly it all worked out well and I only had to make one slight adjustment to one of the holes (which was easily covered by the trim piece). Getting the spring clips in is not too easy if you haven't removed the C-pillar trims and side trim panels.