[bhazard]

You can only dial down as low as your wastegate actuator is set up for. On my tbird, thats 10-12 psi. On the shadow its 4-5 psi and on my capri its around 7 psi.

An adjustable actuator would let you do as people are describing above, you could drop the actuator setting to allow no boost or less than the stock actuator is set up for and use a boost controller along with it for easier adjustment when you want it.