According to the rules (As read in the Conquest rulebook) for pushing multi-dial figs, the push damage comes off of one of the "active" sections.

My question is thus:

If, on the turn you push, you use the front and both sides to perform the push action, can the damage be clicked on the back dial? Or is the term "active sections" only apply to the section you use?

i think only the dial your using

You may apply the pushing damage to any dial you like.

An active section is a section that doesnt show 3 skulls. In this case it would be an inactive section.
If an inactive section is attacked, the attacker may redirect the attack to an active section of his choice.

Just to repeat some stuff.

And more:

Pushing work this way:
If you use actions on a MDF in 2 consecutive turns, the MDF is pushed (1 pushing damage is applied) and must rest for a turn.
It doesnt matter which sections, or how many sections have moved in the two turns.
So if you push, you might as well do it for real.