MIG wrote:
(And I don't think there is any way of avoiding a zone 1 and/or 2
section without touching out and getting a bus, or maybe Silverlink.)

You can avoid zone 1:

change at Acton Town for District Line
Change at Turnham Green for train going in reverse direction
change at Gunnersbury.

Alternative via Earls Court, Olympia, Willesden Junction.

Another alternative via Acton Town, Rayners Lane, Finchley Road then
street level to Finchley Road & Frognal or alternatively West Hampstead
but the interchange there is also street-level. (That is assuming
Silverlink between West Hampstead and Stratford as the Jubilee Line
goes into zone 1)