You can not do it through iTunes. Anytime it tried to restore, it will overwrite your data. Place the iPod is Disk mode
" If necessary, verify that your iPod has a Click Wheel.
Before placing the iPod into Disk Mode, verify that it is charged.
Toggle the Hold switch on and off (set it to Hold, then turn it off again.)
Press and hold the Menu and Select buttons for at least six seconds, until the Apple logo appears.
When the Apple logo appears, release the Menu and Select buttons and immediately press and hold the Select and the Play/Pause buttons until the Disk Mode screen appears.
Illustration of disk mode
Connect the iPod to your computer; the screen on the iPod will should say "Do not disconnect". from here. You can also find a good tutorial about that on here. After that you should be able to access your iPod as a regular additional drive through your operating system. You can of course also try to access the data with software like Copypod etc. Hope this helps,good luck