I'm guessing you would probably need to change more than just the disc.
Not sure what power/torque you're running, but without going to all that expense just changing the brake pads to a higher performance pads might get you what you want.
Difference in r56 cooper and cooper s brakes - North American Motoring
Cooper (non S) - Difference in r56 cooper and cooper s brakes - What exactly is the difference in the brakes between the non-s and s coopers? are the calipers or rotors different?
www.northamericanmotoring.com
Not sure what power/torque you're running, but without going to all that expense just changing the brake pads to a higher performance pads might get you what you want.
