I'm a stingy so I'd gamble and wait until OLCI opens. If I was unsuccessful I'd ask the cabin crew if they could help us out. If that failed I'd then make the most of the flight and look forward to spending the £££ saved on a slap up meal.
OTOH if you feel sitting together is a must then cough up the fees now instead of having it in the back of your mind until departure. A ridiculous situation to put your premium cabin passengers in to be honest.