I wouldn’t say impossible. I have just booked this month our return J flights to Tokyo, going in summer holidays next year.

As they release 4 J on each flight you could split the reward booking over the 2 daily planes or classes? Or 4 reward seats one cash?

My tip would be book online a T-355 days at 1am when seats are released. For the return you can book them online also, and if using a 2-4-1 as I did call/ message to get the avios refunded.

Our backup was flying back from HKG which appears to have less reward demand.

Worth noting that IB have a flight to TYO as well.