Heat gas or charcoal grill. In small bowl, mix blue cheese, sour cream, celery seed and Worcestershire sauce; set aside.
To flatten each chicken breast, place boned side up between 2 pieces of plastic wrap or waxed paper. Working from center, pound chicken with flat side of meat mallet or rolling pin until flattened slightly.
When grill is heated, brush each chicken breast with 1 tablespoon wing sauce. Place chicken on gas grill over medium heat or on charcoal grill over medium coals; cover grill. Cook 10 to 12 minutes, turning once, until thermometer inserted in center of chicken reads 170°F.
During last 2 minutes of cooking, place kaiser rolls, cut side down, on grill; cook 1 to 2 minutes or until golden brown.
Place grilled chicken on bottom halves of rolls. Top with blue cheese mixture. Cover with top halves of rolls. If desired, serve with additional Buffalo wing sauce.