"A blockade of NK is not as easy as we think. It would tie up a good portion of our fleet (over 50%) for years and be terribly expensive."
of course it's expensive and not easy!
but what are the lives of hundreds if not millions of Americans and America's safety and security worth with missles and maybe nukes not to mention the illegal drugs & counterfeit dollars NK exports.
and "years?"...I don't think so, kim jong mentally il won't be around for "years"
There is a cheaper and easier way... I call it "The Khrushchev Option". As we remember, Khrushchev got Kennedy to remove IRBMs from bases in Turkey by his gambit to place nuclear SAMs in Cuba in 1962 as a result of "Cuban Missile Crisis".
[See http://www.spartacus.schoolnet.co.uk/COLDcubanmissile.htm ]
To that end: quietly (but not so quiet that China doesn't see it) start arming Taiwan with more sophisticated weapons and make it obvious that if NoKo continues its nuclear WMD programme, we'll help Taiwan achieve the same goal, at which point they may well declare independence. China would forever lose any hope of the possibility of having Taiwan.
Being on the receiving end of possibility of "Taiwan Nuclear Missile Crisis" should quickly impress upon China that they need to slowly choke off NoKo's energy supply, once the measures are taken to prevent NoKo refugee crisis.
Problem solved, relatively quietly and inexpensively.
Everybody is happy, as China really doesn't want unstable nuclear Kim on their border. It's her problem, much more so than ours. China is in a bit of bind, we can help them save face by applying "gentle" pressure of nuclear threat directly to her forehead (Taiwan). NoKo was her nuclear proxy, Taiwan could be ours.
Taiwan is the best vehicle for this as Japan may not want to become military-nuclear, and SoKo is wobbly (though that may be changing soon) and unreliable partner; there may also be a chance of Korean re-unification and we may not necessarily want nukes there if that happens.