You can make an external ALDA using a 7 psi wastegate actuator attached to the stop lever.It should pull the stop lever partially with no boost but also the stop lever must be able to travel more to shut off the engine.Take a look at this video it should clear things up
Dieselmeken shows outside adjustable ALDA for Mercedes Superpumps - YouTube
Or you could buy one already made by dieselmeken.Priced about 120 eur i think.