I took my rear seats out today to replace my blown seatbelts and pre-tensioners so I had a good look at the seat mechanism. Although I didn't take it right off, The plastic trim at the top of the seat will prise off with little effort. I got a screwdriver underneath and it started to pop off. I reckon you can get at screws to be able to take that whole mechanism out. If it was mine, I would take the seat out and give it a go, you never know you might be able to repair it. If you can get it out you could pick up a rear seat back on eBay for about £40 and swap the mechanism over.