I think this is really a question for the AA forum, but some thoughts...

You mentioned 25% miles and 25% bonus on YVR-LHR. Half right - no plat bonus on BA.

Don't forget that the challenge is good with any AA flight number (not just AA metal) so you could rebook SYD-HNL as the AA codeshare and include that in the challenge. Also you could look at a separate west coast itinerary on AS using the AA codes on many of their flights - they wouldn't use RTW coupons but the Q-points would count for the challenge. AS round trips to SEA or YVR from LAX or SFO are not terribly expensive.

If it were me and trying to make the most in mileage from an LONEx I would look to drop a segment or two someplace (maybe use an airpass in Asia or Oz) and end up with ORD-AMM-LHR using the AA code on RJ and then RJ metal back to London.