you can go to a lower boost setting by taking off the connector from the amal valve, but not to 0 boost. this may well be low enough for your test.

the only way to go to 0 boost is to open the wastegate completely. you can either do that by pressuring the actuator somehow, or as suggested, removing the actautor rod from the wastegate spindle. that is the easiest way, as you just have to remove the clips and pull it off. refitting is the reverse of removal.