Tried hipmunk, no luck, didn't even offer the routing.
Thought about a travel agent, but decided to stay another night in Tokyo.
Buying one-way in PE LHR-AKL, then AKL-NRT, cheaper to buy another night's accommodation, cancel partner's redemption ticket on BA in PE and for us both to get redemption tickets on JAL in PE HND-LHR the next day. Perfectly acceptable for long all day flight on JAL 77W, with lounge access in advance.
Now considering about whether it is better to go LHR-SFO-AKL on VS/NZ (with NZ codeshare on the VS flight) to use the Clubhouse at LHR (which is good fun), or cough up £150 more to go NZ the whole way, in PE via LAX. Will have dropped to Gold by then, and have 2 new RUs, will spend on going PE-BP from SFO or LAX-AKL, spend the other on upgrading AKL-NRT from Y to PE (it's a 77W on that day oddly).