I ended up mixing a small can of diced fire-roasted tomatoes with some red wine vinegar, a wee bit of brown sugar, garlic, paprika, cayenne, black pepper, and salt in the crock. I then rolled the beef shoulder roast in it, and topped it with onions and carrots. It will now marinate in the fridge overnight (the liquid almost reaches the top of the roast and I put some of it on top of it). I added frozen green beans during the last 1/2 hour.