Pour the vegetable oil into the bottom of a slow cooker. Place the pork roast into the slow cooker.
Combine the barbecue sauce, rice vinegar, and chicken broth and whisk together. Add the brown sugar, yellow mustard, Worcestershire sauce, chili powder, onion, garlic, and thyme. Whisk everything together and pour over the pork roast.
Cover and cook on high for 5 hours. Let roast sit in crock pot on warm for up to an hour, then shred the meat with 2 forks.
Strain the sauce and discard solids. Mix a teaspoon of cornstarch with a small amount of water to make a paste. Continue adding water, a little at a time, to make the cornstarch mixture thinner. Add cornstarch mixture and strained sauce to a saucepan and bring to a boil. Simmer ten minutes or until slightly thickened.
Pour half of the sauce into the shredded meat and combine. Add more if needed, serve the remainder on the side.
Optional: Spread the inside of both halves of hamburger buns with butter. Toast the buns, butter side down, in a skillet over medium heat until golden brown. Spoon pork into the toasted buns.