I was thinking about this and here is what I am going to try.
a electronic one...........
like this. take a voltage reading at the input of the turbo VGT solenoid and find out what it is at you max boost that you want.. like say 30 psi = 10 volts (just making this up for now) then put a revising diode to limit the voltage seen at the turbo to that amount so that no matter what you computer tries to push the turbo to it will only see you max setting. should keep it under 30 ??
I have not put any leads on mine yet, working to many hours at work right now, but a friend who is a I&C tech at work is going to make it for me when I give him the voltage I want stopped.