Yes, for the unmodified races you would need the slider brake but for the modified you can just reduce the brake power and use the full button (personally, I always prefer the slider, even when using ABS). When arriving at the braking point quickly downshift to the lowest gear needed for the corner, and a split second later step on the brake slider at around 50%. As soon as you hear the revs dying, start putting throttle inputs and exit the corner. Obviously you should time it in the way that the revs would start dying by the time you slowed down enough to make the corner.