On another forum I read for Primo users, of which I am one, a user made a really great suggestion. I have tried it and think it is a very nice technique. His name is Char-Woody.
He suggests taking the trimmings and cut them up into smaller pieces. put them into foil that is as long as your brisket and season with your rub, if you like. Roll the foil into a pouch and puncture one side of it lengthwise with a fork. On the Primo, we use our upper racks to place this fat packet with the holes facing down. The brisket goes underneath it and as the fat packet melts, it drips down on the brisket and gives it a great crust. So you self-baste it with its own fat. I usually cook mine with the fat side down to keep the non-fat side tender. This adds a fatty layer to the all-meat side.