If you sometimes want to start in 1st and sometimes want to start in second the only device that will work is the shifter that MB provided. Here is a trick for you, come to a stoplight and while holding the brake just lightly enough to keep the vehicle still at idle, notch the shifter over into 1st. You should immediately notice the car idling forward through the brake you were holding. Once you have notched it over to first it will stay in first until you get moving. With light throttle it wont stay there long but more foot should keep the gear nicely. The tuner tranny valve bodies are something that once changed, will be that way as long as they are in the car. Since the tranny has no electronic "brain", as do the later cars with the 5-speed auto, the only way to change its behavior is with the shifter or a valve body.

Hope this helps...Lee