In a bowl, combine whole wheat flour, rice flour, baking powder and celery. Using a pastry blender or two knives, cut in cheese and margarine until mixture resembles fine crumbs. Stir in sesame seeds. Gradually add water, mixing with a fork to form a stiff dough. Form into a ball.
On a lightly floured work surface, roll out dough to a thickness of 1⁄8 inch (3 mm). Cut into 2-inch (5 cm) squares. Place on prepared baking sheet.
Bake in preheated oven for 8 to 10 minutes or until very lightly browned. Transfer wafers to a wire rack and let cool for 2 hours. Store in an airtight container at room temperature.