Prepare the smoker for indirect heat, between 225 and 275 degree F. Make four to six foil "rings" by taking a thin strip of foil, rolling it tight and securely connecting the two ends. Set the foil rings aside.
While the smoker heats up, prepare the onions. Slice off the root of the onion, to make a flat bottom. Make sure to remove the roots while keeping the hardy base of the root intact. This will ensure the onion maintains its shape and keeps liquid from leaking out. Cut one inch off of the top of the onion. Using a spoon, scoop out the inside of the onion, leaving a 1/2-inch wall of onion and creating a hollowed-out, bowl-like onion. Set aside in a casserole dish.
Lightly coat the exterior and interior of the onions with olive oil. Add 1/4 tsp of kosher salt and 1/4 tsp of barbecue rub to the onion (exterior and interior of each onion).
In a medium-sized bowl, thoroughly combine the cooked sausage, cooked rice, bell pepper, cream cheese, vinegar and 1/4 teaspoon of salt. Taste the mixture and adjust the salt content. Add the rice and sausage filling into the onions. Top the onions with the butter pieces.
Place the foil rings onto the grill. Place onions onto the rings and smoke for 1 to 1 1/2 hours, or until the onions are softened but retain their shape. Remove the onions and serve warm.