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There was a thread with a pic of the back headrests folded, with a comment that it was nice to be able to get them out of the driver's way... so I suspect they do. Not sure if seat or rear-decklid mounted though.
EDIT: Not on the decklid: Back Window Pic. Man they sure don't look foldable.
On the S you just have to make sure the front seats are far forward enough for the swing. You can usually put them back a bit again after folding since the backrest tends to be angled (depending on the seatee).