Buy enough SPG miles to get you to 40k, then convert them to 50k Alaska miles. Depend on season, coach tickets on AA from Japan to US would go for 25k miles off peak (and 32.5k peak). Alaska allows stop overs, so you should be able to add a tag flight from Hawaii to US Mainland on either American or Alaska for no additional points (only taxes).

If you are flying during peak season, buY 10k miles from Alaska to get you to 60k and that should be enough to get two economy tickets on Japan airlines from Tokyo to the Hawaii, have a stopover, and continue to DEN (via either PDX or SEA) on Alaska