One word: Don’t. (Well, that could be two words if you consider a contraction two words. Either way, don’t do it.)
We shouldn’t be persuading anyone to do anything they don’t want to naturally do. We shouldn’t take the viewpoint that we know better than they, and they just need to be guided into the light. Scientists do share data, but with other scientists that they want to share with. Convincing them to share with anyone and everyone is a misguided tactic, at best, and a complete waste of time, at worst. Sure, there is value in sharing data sets among scientists, but we must realize that there are more important issues to tackle first, such as basic data management skills and long-term preservation file formats.