Stir together light mayonnaise and next 4 ingredients in a medium bowl. Stir in cheese.
Spread 1 tablespoon cheese mixture into each celery rib. Garnish, if desired.
Note: Store remaining pimiento cheese mixture in an airtight container in refrigerator up to 1 week.
Don't be tempted to use preshredded cheese. It takes a few more minutes to shred your own, but you'll be much more pleased with the creamy texture.