You need a simple a air switching solenoid. All it will do is divert the boost reference port, off the charge pipe, compressor housing… or where ever you have the wastegate or your manual boost controller hooked to. With the solenoid in one position, it will send the boost reference to the waste gate only, allowing you to boost to wastegate spring pressure. then with the solenoid in the second position, it will divert the boost reference to the manual boost controller, then to the wastegate. You will also need to T in both the out put from the MBC and the output from the first position on the solenoid into the waste gate port.