In short, no you can't.
The 1.8T engine uses a recirculating boost system so the excess charged air from the turbo is fed back into the system when you let off the throttle. Since the air volume is measured before and after the turbo, any fluctuations in these measurements can cause running issues for your car.
You can however fit an uprated Diverter
valve so long as it is a recirculating type, such as the 007 range from Forge Motorsport
If you fit one of these along with an induction kit, the noise of the air being dumped back into the turbo will be louder and closer to the 'whoosh' noise of Blow-off type DV's. An uprated turbo inlet pipe from the likes of Samco or Forge will also result in a louder dumping noise and a healthy whistle from the turbo as it spools.
If you really do have your heart set on making your Golf sound like a Subaru then you can try
a semi recirculating valve known as a 'Splitter' available from Forge here http://www.forgemotorsport.co.uk/content.asp?inc=product&cat=1703DV&product=FMDVSPLTR
However, several independent tests of these have still resulted in running problems since there is still a conflict in the air volumes. These tend to work better on the earlier 150bhp AGU engines as they only have one sensor before the turbo to measure air volume, whereas the later engines (2000 onwards) also use a map sensor in the intercooler. If you find that this type of valve is causing you problems, Forge (at the time of writing) will no-hassle exchange it for a fully recirculating valve.
Here at GolfGTI.co.uk we would not recommend anything other than a fully recirculating valve.
Hope that clears up some of the myths and reduces the amount of times we get asked this question