The only answer is to remove him (Kim Jong Un) from power, but this is easier said than done. The population sees him as some sort of god and Korean military leaders fear him. Yes, China might force him into line, but the truth is we have very few options short of war.
Here is one interesting option that just might work. Let's just let the people of North Korea throw him out of power. How, you ask? By proving that his lie to the people that the world is against them is just a lie to justify his actions. We do this by dropping rice bags daily on the rural area to feed the starving population.
These bags are imprinted with "Compliments of the U.S., Japan and South Korea" and in time they will see through his lie. Once this happens the military leaders might step up to plate and take charge of the situation doing what is right for the nation.
Sure it long shot and will take time but it's worth a try and beats war.