What are China's options?
Reduction of aid? What else?
An effective an easy option that could begin immediately would be border control. As of now, China quietly allows the North Koreans to smuggle missile parts and luxury goods across the Yalu. They also often turn the other way when both "wealthy" Koreans and impoverished young girls sneak across the border. The former goes into China to shop, the latter goes to become prostitutes. They both bring back badly needed foreign currency. LINK LINK LINK
A more long term option would be to put more controls on Chinese banks that finance the Kim regime's less immediate concerns (e.g. aid for food and electricity). This would have the added bonus of severely curb money laundering, counterfeiting, and drug dealing. They could also stand aside and let the U.S. Treasury Department do the same. This doesn't require UN approval, but the U.S. has been reluctant to do it because of the ramifications. This has been done before with mixed results, most notably in 2005 when Treasury sanctioned Banco Delta in Macau, causing a major run on the bank.
Another option would be to require (as the West and South Korea do) the nuclear issue to be part of any further multilateral negotiations.
The options are limited, but they are greater in number than our own. They could effectively alter North Korea's behavior without inducing the ever-feared Korean horde of starving refugees from crossing the Yalu.