I don't believe there's anything you can do with the stock turbo to induce the boost to come on earlier in the RPM cycle. The only mod I'm aware of would be to find a way to produce a higher amount of boost by delaying when the wastegate begins to open. As has been mentioned, this wastegate is vacuum operated. The valve is normally open and requires a vacuum signal for the gate to shut completely, and thus allow boost to build. The gate begins to open up when the vacuum signal is gradually reduced as the engine computer senses that maximum boost is approaching.