In a large bowl, whisk together flour, sugar, baking powder, and salt.  Cut margarine into flour mixture until it resembles coarse crumbs.  Add in rice milk, lemon juice, and lemon zest and stir until dough comes together.  Knead dough for 1 minute, adding more flour if dough is too sticky.  Add blueberries and gently knead together for another 30 seconds.  Divide dough into two balls and press each into a disk about 1" thick.  Use a knife to cut each disc in quarters.  Place scones on a baking stone.  Bake at 400 for 17-22 minutes or until golden brown.  Whisk together lemon juice and powdered sugar to form a glaze.  Drizzle over warm scones before serving.