I smoke in my weber a lot. I put the charcoal baskets on each side, put the flip op sections of the grill grate right over that so it's easy to add more fuel and smoke wood. Then put the meat inside a high sided disposable aluminum tray to act as the heat sink. Poke holes in the bottom to let the fat drain out.
That being said, that ring would make the process much easier. With the method I use, I have to add a couple charcoal briquettes to each side about every 45 minutes. Gotta constantly monitor the temp to keep it low enough in such a small space. That Ring would essentially more than double the interior size of the space.
My FiL has a weber from about 25 years ago that came with a ring like that. I'm not sure if Weber makes them anymore specifically for this. I'm guessing that self fabrication is the only way to go here...