[Elgin Clock]

<edit>
For the pneumatic portion, squirrel has a great idea below my post.

For the elctrical portion the following applies:
</edit>

The only effective way of dealing with this scenario that my team has used in the past is to have as much cable as you need to use to extend the full length, and then arrange it (very neatly) in some wire loom material or whatever so all the cable is covered from damage, and then use some sort of spring (surgical tubing or whatever) to hold it so it stays in a safe place when your arm is retracted to the minimum length.

Basically do anything that works, but also keeps the cables away from any pinch points, and use enough cable to not pull the cable out when you are fully extended.

I don't know of any cable that has "bungee" qualities as of yet.

And, this is not only coming from a team standpoint, but from someone who works in a cable assembly department at an Engineering firm.

We use so many cable types, it's unbelieveable, but as I said, nothing meets that magic "bungee" requirement that would be the best way to run cable.