dude, y don't u try some aftermarket sequential blow off valves? Seqential meaning venting the pressure internally and also venting into the atmosphere. A lot of these BOV's make the fluttering sound you desire. Since you are in Melbourne AVO in Cheltenham make their own and also the HKS super sequential Blow off valve is a good choice. There are many others out there but those are just some examples. But remember that any BOV that vents to the atmosphere does not pass emissions and if u go around parading yourself you'll get defected. Doesn't really matter tho if it ever does happen its just one pipe and u replace it with the stocky intercooler piping.
hope i've helped a bit.