It is definitely worth asking again at check-in and again at the gate, as seat assignments can move around, even last minute. On an international flight, there are often people upgrading from PE to J, and they are often in decent seats. I have had success with some version of "I noticed that there seem to be a couple of people upgrading from PE. If they are successful, could you try and get me into one of their non-middle seats". I may have just been lucky, but have never had to fly in the middle seat.