Put the pulled pork and broth in a 4-quart slow cooker and toss to moisten it.
Cover and heat on low until the pork is steaming throughout, 1 to 1 1/2 hours.
Whisk the mayonnaise, vinegar, horseradish, mustard, Worcestershire, garlic powder, black pepper and salt until smooth.
Refrigerate the white sauce for at least 20 minutes so the pepper and horseradish settle into it.
Toast the cut sides of the buns in a dry skillet if you want a sturdier sandwich.
Fill each bun with hot pork, spoon on the white sauce and finish with a loose handful of cabbage.