Get a Pod Filter, and then take off the bov and block off all associated pipes. DONE!

Beware though... Doing this causes your turbine blades to rapidly deccelerate when you close the throttle. This rapid decceleration puts a fair bit of pressure on the bearings on the turbo. Running no BOV will significantly decrease the lifespan of your turbo. But dont worry, TD04 WRX turbos are cheap. Of you can afford to replace it when it dies, go for it!