I don't know for sure what the standard exhaust set up is like (one piece of multiple) but If there are no options the simplest thing for you to do is to have the Cat cut out and a pipe welded in place of it. I'd be careful of where ur lambda sensor is though, if its pre-cat you'll be fine, post-cat and you'll need an O2 cheater or something similar to trick the lambda into thinking your air fuel ratios are correct, or adjust it to read slightly differently (not sure..) I know with the 20VT's you can change the turbo downpipe.
Realistically though, if your upping boost, you need to derestrict your exhaust system to allow the turbo to flow easily through the system. Removing the cat will help massively, but with turbo applications in particular, bigger will always be better. Keeping the standard system with increased boost levels will just restrict the turbo. Peak boost will probably big mid-range and it may even lose boost in the upper RPM region
