You just need a PWM valve (an idle valve for example) correctly sized and controlled by an ecu or simple circuit to give enough flow bypassed to atmosphere to lower the boost to the required ammount. No need for wastegates or anything complicated.

I'm assuming your plumbing will be

Air filter - charger - intercooler - throttle - inlet manifold

if so, just fit the vent valve between the charger and the throttle.

You wouldn't be able to get away with this on something like the eaton which is positive displacement.

An alternative would be to use a clutched charger and switch the clutch on and off rapidly to give the required boost (PWm again). Most charger clutches would burn out quickly doing this tho.