dude... first of all, listen to your parents. you may think you're awesome and know everything but you don't.
second of all, getting a workout comes from going fast and long and hard, not from how much you brake or what you brake with. go to a trail or bike path(paved, of course) and just bike for hours at a time. that's the best way to get a workout, not riding to your friend's house in your parent's suburb without brakes.
screw brakeless riding, especially for people with their first fixies.