He might have made sure the guy kept his hands out of his pockets from the very start. Other than that, I see nothing he could have done short of questioning the guy with gun drawn the whole time.
See, this is what pisses me off so bad about the Ferguson protests and other crap. You can take an isolated incident like that and turn it into an explosion of racial tension, when their should be none. But cops put their lives on the line every single day and this stuff has long since become commonplace. Where's the marching for this 24 year old guy who lost his life just for doing his job?