Problem with linking both ends..

Hi guys. I am currently trying to make an animation but im stuck with an issue.
If you take a look at the attachment below, you see two spheres, a box and a
path. What i want is to be able to move the left sphere01 to the right along the
x-axis. While this happens, the sphere02 is supposed to follow the path upwards
and the box inbetween is supposed to always stay centered between the two
spheres. So that when you slide the left sphere to the right in the x-axis, the
right sphere moves u
p along the path and the two ends of the box always follow the two spheres. Is
this possible? I know i can use linked x-form, but that messes with the shape of
the box, and this cant happen. Any suggestion? Kinda hard to explain :)