basically, you can't. ok, I'll try and explain better this time.
the lowest psi the turbo can run at is determined by the spring of the waste gate. e.g. the stock one lets you run 5 psi, and 5 psi is the minimum. even if you have an electronic boost controller, you can turn the boost up, but, even if you switch the controller off, it will not go below 5 psi.
You can have no boost by disconencting the wastegate actuator. This means, no boost at all. You cannot have boost unless you reconnect it.
an r33 gtst is quite easy to drive, especially with stock turbo. Just don't press the accelerator hard, and it won't accelerate hard. it won't even come onto much boost if you give it a decent press. You basically have to floor it to get 5 psi. the boost comes on very linear on the rb25, compared to something like a sr20. So, to answer your question, I guess try not to think of it as boost. people get scared by the term boost. Think of it rather as just how much acceleration you want, more = press harder, less = press less (boost is quite linear in rb25).