Is it that you don't want to use store bought BBQ sauce or are you not wanting to put any sauce on them at all?
Recommend reserving 3 Tbsp of the dry rub you use for the brisket. 2 Tbsp for a spritz during the cook, and 1 Tbsp mix with a 1 Tbsp of brown sugar. Cube your burnt ends when done with your cook and either sprinkle/toss burnt ends with the dry rub and brown sugar OR mix the rub and brown sugar with several Tbsps of butter and then toss with burnt ends. Throw back on the smoker for another hour or two to get them barked up.
Or, make your own bbq sauce out of brisket fat trimmings, vinegar, ketchup, few Tbsp of your dry rub, butter, brown sugar, fresh lemon, garlic and onion, let simmer/render; toss cubes in that and back on smoker for couple hours.