While you can't make it impossible to use the Internet on your iPod, you can make it pretty inconvenient (which should help with the self-control thing!):
Firstly, you can change your WiFi password to something really long and complex that you won't remember off the top of your head. Keep the password written down somewhere obviously, and save the password in the keychain of devices you DO want to use the Internet on (such as laptop, iPhone etc). So if you get the urge to go on the Internet you won't just be able to flick on your iPod's WiFi and start browsing - you'll need to go and find the password.
Another thing you can do is download Springtomize (it's a jailbreak tweak) and use it to disable the icons of all the web browsers on your iPod (which pretty much makes it so you can't open them). You *can* go into the settings and enable it again, but seeing as you have to respring and all it's quite a pain. If you're going to do this there's also a JB tweak that disables spotlight which you should get, as even if you can't open Safari via the icon you could still search it up on spotlight.
Hopefully if you do both of those things then the bother it will be to get on the net will make it easier to overcome your Internet addition 😀