no...a trans BRAKE is a device installed in the valve body that will apply fluid pressure to several sets of clutches and bands at the same time....basically locking the transmission down. it allows the engine to build boost while staged, since the engine will be under a heavy load.
trans brakes are on drag cars for a reason...you leave the line at full engine power. also meaning you will break stuff....alot.
why do you want a trans brake? do you know the death and havoc you will wreak on your car?
www.levelten.com can do one, last i heard. i have not seen one installed on a WRX though.