Can I have a slider impact a timeline just at one point?

I am using AE CS6, on an HP 820z, Win 7.

I would like to have a series of layer objects follow different paths to an end point where they line up horizontally curving back in space on the sides.

Here is a small example:

But at the end point, I'd like to be be able to use a slider to adjust the x, y, & z axis. For the z axis, I'd like the orb of each layer pairs to fall behind the one in front of it on the z plane.  I can't figure out how to write an expression for that. Also I'd like the y axis to follow a besier curve that extends symmetrically to the right and left of the comp mid point.

This is what I have to separate the x axis but I can't figure out how to connect the y axist to a besier curve or to make each layer pairs ahead of it.

jeff

[thisComp.layer("Trajectory").effect("X Offset")("Slider"),transform.position[1],transform.position[2]]