For Europe & UK, ANA has F class metal only for FRA and LHR to HND flights. Also, only one seat is released initially, so tough to get 2 F awards. One F and one J would be feasible, with potential for a change J>F but not able to waitlist. Book the flight as HND-LHR outbound (any earlier date), LHR-HND inbound (on your preferred date) then change the HND-LHR leg to your desired HND LHR inbound date when this appears.