most straight forward way is to put a bigger diameter pulley on the supercharger, making in spin slower in relation to the engine, and produce less boost.
you could just put a bypass pipe that goes between the inlet and outlet of the sharger (no valves or anything though) just a pipe (20 -30 mm?????)
dunno, just design your engine to cope with the more boost, or take off the charger until you can do it properly??