You can use a leg wrap to stop mid-rappel. To create a leg wrap, hold the brake line with one hand while wrapping the brake line around your thigh several times. The friction of the rope wrapping around your leg should be enough to lock off your rappel device and halt your descent.
The leg wrap is quick and easy and can be used with most rappel devices.
The leg wrap should only be use for short periods of time because it is uncomfortable.