Thanks a lot, fordmar,
The two key elements are that a spline can be a Field and that the MoSpline can be used to adjust how that spline affects the scene (Start, end, Offset), while the other is when the Clone with the Ridged Body appears, Dynamic takes over. If that goes too fast, the Blend might not do it completely. I used the MoSpline (a copy) for the MoGraph Selection, which then went into the Rigid Body as a "switch".
Let me know if you Have questions.
Enjoy