wow, that's some grainy picture
bit hard to really tell anything from that...
see the two white lines going left to right (and slightly up)? looks to me like you need to strap the central locking motor's output arm to the top one of those. finding the ideal place to mount it is the next key. Unless the door is designed for it, it's very hard to tell from the picture. You'd have to get the motor and and open the door to have a play around with mounting arrangements.
So with the back doors, there's no cable transfer device?