According the Boeing web site, the first commercial 707 type jets were the 707-120 series of 1958 which had a range that was barely sufficient for the Atlantic Ocean. The 707-320 series in 1959 achieved a range of 4000 miles with 141 seats.
True, but it's less than 3,000 mile to either Seattle or San Francisco. They'd have to refuel anyway, if they wanted to get to Boston or other Northeastern city. So might as well carry passengers from Hawaii to one of those, and passengers from there on to the final destination.
Fortunately the routes from the US west coast to the orient, mostly go up near the north pole, and that route is actually mainly overland. Refueling in Alaska is practical as it doesn't require that much deviation from the great circle. Flying to Australia or New Zealand, you can stop over on any number of Pacific islands, including Hawaii. IN both cases with some deviation from the great circle route. North of it in both cases.