1. Stir the picante sauce, Worcestershire, vinegar, molasses, coffee, cocoa powder and garlic in a medium bowl. Pour half the picante sauce mixture into a 3-quart shallow, nonmetallic baking dish for marinade. Cover and refrigerate the remaining picante sauce mixture.
2. Add the ribs to the baking dish and turn to coat. Cover and refrigerate for 12 hours.
3. Set up the grill for indirect cooking. Lightly oil the grill rack. Heat the grill to medium. Grill the ribs for 3 hours or until fork-tender, turning and basting often with the marinade. Discard the remaining marinade.
4. Heat the remaining picante sauce mixture in a 1-quart saucepan over medium heat to a boil, stirring occasionally. Serve the sauce with the ribs and sprinkle with the onions.