OK.

I have been looking at this. And I might have a solution for you:

Try using the Constrain>Geometry Option and once done you should be able to move on curve along the length of the other. Or if you want (which I think you do), you select the main curve and both will move together.

Remember to get the effect right you will have to ammend the pivot point on one of the curves.

Hope this is what you are looking for.