Prevent iPod from mounting as a disk?

I have an iPod Classic. When I connect it to my main iTunes Library, I had set it to manage my songs manually. So it now mounts as a disk and shows the "do not disconnect" icon.

Trouble is, when I am at work I want to connect it to the USB port on my MBP just to not run down the battery. I have no songs on my Mac there. I listen through the headphone jack on the iPod and use its controls. But one I plug it in, the screen changes to the "do not disconnect" screen and I can no longer use it. Sometimes it does not show up on the Desktop, so I can't "eject" it to use it as an external iPod.

How can I disable this mount as a disk behavior for this iPod?