i would save you the trouble and just buy a used one.

but if you really want to take the risk.

use a ball pean hammer and dent in the center of the by pass valve. thus it will compress the spring more. so you can in theory hold more boost.

personally i think this is a very Gehto way to do it. and you could do some real bad shit to your system if done wrong.

make it work right the first time. buy a aftermarket one.