I can think of two ways to controlling the rod length.
1. Positive biasing the rod position voltage at pin #4. to the control loop should extend the rod and lower boost.
2. Positive biasing the T-MAP sensor.
3. Combination of the above.
I will set out a method to make this happen. I notice BMS sell a male/female plug for this wastegate sensor. If you can purchase one of those, I will pay you back. This will make life a lot easier.
http://www.burgertuning.com/N55_JB4_upgrades.html