Try openly producing and selling. Multi-million dollar businesses operating in open plain view of the public and any federal agent. States legalize cannabis and the federal government in turn stops enforcing their laws against cannabis in those states, demonstrating that the states have de facto sovereignty to legalize drugs. They didn't just stop prosecution for "basic use" and possession, they no longer enforce their drug laws against growers and dealers either. They've essentially given up, for the time-being at least.

The fact that the same states are not also defying federal gun laws (with some interesting exceptions *cough* alaska *cough*) is another matter entirely. The federal government does seem to be more keen on exercising their sovereign powers when it comes to guns than with drugs.