How make a 'null path' - center of objects following path

Question

What I mean: https://youtu.be/vHXavxVEfGk

Can I do it? I want (invisible) null path to control objects position (but no rotation)

Answer 1

If somebody interested - I did it with 3 nulls and expression. Probably it's not best way to do it. Paste below code in elements position

1st and 2nd null - start and end point of path
3rd null - only for controling X-axis

Tx = transform.position[0]; 
Ax = thisComp.layer("null 1").transform.position[0]; 
Ay = thisComp.layer("null 1").transform.position[1]; 
Bx = thisComp.layer("null 2").transform.position[0];
By = thisComp.layer("null 2").transform.position[1];

Ty = (((By - Ay) * (Tx - Ax)) / (Bx - Ax))+ Ay; 

[Tx, Ty]