The winds at flight levels over the Eastern Pacific are predominantly westerly. Summer flight times are closer to even going both ways, but still a good half-hour to an hour different a lot of the time. That is, faster flying from Hawaii to the US Mainland.
In the winter time all bets are off. Can recall one HNL-SFO leg that was 3:58 wheels up to wheels down AT MACH .80. Think about it. The return flight the next morning (SFO-HNL) was almost 6 hours. Have seen a 7:02 flight time from SEA-HNL against a nearly 200 knot jet most of the way.
The tradewinds usually die out at the inversion layer, which is usually around 8000 feet near Hawaii most of the year. A common profile is a 20 - 30 knot northeasterly trade from the surface to 8000, calm from 8000 to 12,000, light westerlies till FL250 or so, gradually building into whatever the jet stream has on offer all the way up to FL4XX.
In a light plane you could in fact have a tailwind both ways a lot of the time if you find that inversion. Fly high going west to east, and fly low going east to west.
But bottom line just pull up FlightAware and look at the region. Click on random aircraft gong each way, and look at the groundspeeds and planned flight times. That should correlate with whatever the wind charts are at the same time and provide all the evidence he needs. If that doesn't work then just go drink a beer and forget the whole thing.