jabbado:
I think it's can be simpler than that. Just have a long shaft with the spirals milled all along it. Then you put "stops" along the shaft where required. Bit hard for me to explain but if the stops are just either side of a "X" part of the spirals it basically turns that location into the end of the shaft and causes the cam follower to reverse at that point.
If you have spirals cut in both directions, there will be a cross-over every time they meet. How do you ensure that the follower keeps going across these rather than reversing?