[chrisi]

The reason why we recommend the DC Interface for powering stuff is because it's fused with a 500mA fuse. So if anything goes south, like a short circuit, that fuse will protect the Field Kit and in the best case scenario also your Arduino.

You can technically absolutely power your Arduino from the Analog or Switch Interface but you are not protected that way and any errors you make might result in a damaged Field Kit or Arduino.

So your idea does work, try it out. But be careful!