Quite possibly. I managed a similar feat (all be it in F) on the 380 when our 4A & 5A seats became 5A and 4K on check-in. A quick word with the desk agent and a phone call to "upstairs" had it sorted. We were told to proceed to the Flounge and our new BPs were waiting for us.
And if check-in can't get it sorted, the cabin crew may well be able to have a quiet word with others (but convincing someone else to move to the back of the J cabin may be a bit of a stretch).
It sucks, but of course convincing someone to take a seat closer to the front of the cabin mightn't be so hard - if you're asking someone for a favour the logical thing to do would be to give them the better seat especially if it's so important to sit with the spouse.