I don't think the third-party numbers are high for Alaska; the state has a long history of third parties doing much better than the national average. Also, the current governor was elected as an Independent. Here's a (partial?) list since 1968:
1968: George Wallace got 12.1% in Alaska, a little less than the 13.5% he got nationally but quite high for a non-Southern state (and Alaska is about as non-Southern as you can get!)
1972: John Schmitz of the American Party got 7.2; nationally he got 1.5.
1976: Roger Macbride (Libertarian) got 5.5, nationally 0.2
1980: John Anderson 7.0 (6.6 nationally); Ed Clark (LP) 11.7 (1.1)
1984: David Bergland (LP) 3.1 (0.2)
1988: Ron Paul (LP) 2.7 (0.5)
1992: Ross Perot (Reform) 28.4 (18.9)
1996: Perot 10.9 (8.4), Ralph Nader (Green) 3.1 (0.7)
2000: Nader 10.1 (2.7) Pat Buchanan (Reform) 1.8 (0.4)
2004: Nader 1.6 (0.4)
2008: Nader 1.2 (0.6)
2012: Gary Johnson (LP) 2.5 (1.0)
Not impossible then, although I'd still be surprised personally. I'd say the Johnson 15 is more likely than the Stein 6.
I wouldn't say that Stein capturing 4-5% is unreasonable in Alaska, where there has long been a relatively strong and active statewide Green Party, and additionally most Alaskans are resigned to the fact that by the time they finish voting the election has usually been called in the Lower 48 once the West Coast kicks in, and then compound that with Clinton's relative weakness in rural parts of the Western United States, and it is feasible, although not particularly likely to see Green leaning Dems deciding to "vote their conscience" if they consider Clinton to already be a shoo-in and that AKs (3) EVs won't be a potential swing vote in a tight race.
