I have been a home roaster for quite some time. While it can be quite simple, to do it right, there are a lot of variables. It can be as simple as a cast iron skillet over a campfire, but the cowboy had to constantly keep the beans stirred, or a very uneven roast will occur. You could put a cast iron skillet on your grates and heat it up good and do it like the cowboys, but you would not really get the smokiness I believe you are hoping to get. As was posted above by Wilpark, there are people that have made, or bought, chambers (barrels) that allow the beans to constantly rotate, either by hand or motor, such that there is an even roast and you would get some of the characteristics of the smoke. It would be interesting to try in in a smoker, but there would be some trial and error over time, as roasting, like smoking, has to do with the variables. Things like coffee batch size, Preheat temp, and rate of rise on the beans, airflow, drum speed, and then finally the all important bean temperature, will produce either good, bad, or indifferent results. There are different roast levels on beans, the lightest being what is called "first crack" where the beans actually pop, like popcorn (they just don't explode like popcorn), and that happens around 170-200 deg (bean temp). And you go darker from there. But, bottom line, as stated before, this would be like learning to smoke on your grill. A new challenge, and doable with some effort. I would be interested to hear if someone that takes on the task, as most people that roast on grills, do it on gas or charcoal grills. Happy Roasting!