The same way N. Korea does everything overseas, foreign agents and "diplomats" that act couriers. China would be the obvious conduit as bitcoin is widely accepted there.

North Korea has the world's #2 and #3 economies next door, and both increasingly like Bitcoin. China has a significant appetite for Bitcoins, even more so with the capital controls now in place. That's a pretty easy black market trade.

I'd venture to say #3 has no love lost for N Korea so highly doubt #3 would look kindly at aiding and abetting N Korea. #2 is rather frustrated with the DPRK regime and have tightened commerce with the regime.

Sell them on one of the Chinese exchanges for yuan and physically carry it over the border to NK.

Hell, you don't even need to carry it over: anything you want to use the money to purchase is going to be in China anyway.

It's trivial to exchange Bitcoins anonymously to cash almost anywhere in the world.

By cash do you mean physical money, like coins and notes, or liquid amounts in a bank account? The problem is physhcal money is not a good way to move large amounts around, and most bank accounts have a great deal of oversight.

No-one cares about $75 being used to buy heroin on The Silk Road, but people will notice $75,000,000 being moved - and Bitcoin is not anonymous either, merely psuedonominous.

Not in volumes that count

$100k over a few weeks and exchanges shouldn't be too noticeable. Especially if you use personnel from several embassies.

$100k in a single trade would not be noticeable.

I'd go with more like $10M over a few weeks.