I dont see any post maf re-placement. He cant be dumping to atmosphere as then he is dumping already metered air and the car would run like total crap. I am guessing he has the stillen bpv on there and placed that ricer valve on there with a stiff spring setting (as not to open under idle) to get the BOV pop/ting of the HKS for the fraction of a second it would be open at decell to relieve pressure in the intake pipe. Which would still give the car a slight, unwanted blip.
Why do you want to do this? Simply for the sound? If you want to let people know you are supercharged then get my kit and the Tial bpv I sell with it and keep open dump. It will be MUCH louder than that HKS.
BTW..hks is now a chinese garbage company since they sold out from US a few years back.
**edit** Oh wait look. You can see the T fitting where he tapped into the vacuum source from the other (stillen) bpv. That confims my theory....LOL.. so much lameness on this.
Nothing like spending a few hundred dollars to sound like a cartoon!