If you are using a Mac it is possible. I'm not sure about a PC.
Turn on the manual manage feature in the iPod prefs (in iTunes). Then you can drag all your tunes to your iPod and then delete them from your computer HD. When you re-attatch your iPod to your Mac, it will not automatically re-sync with iTunes, so you won't lose all your songs.
A word of warning however - if your iPod malfunctions all your songs will be gone forever, never to return. It's best to have a back-up of them somewhere.