http://filetrip.net/...rader-6-60.html
Works on 5g Go, can't remember if it support anything newer.
Edit:
Yes, I mean it is a downgrader to 6.20, from there you can install a 'permanent' hack.
Nothing hard about it, put the downgrader in the game folder like any other homebrew, and the 6.20 update file in the update folder like any firmware upgrade and launch the downgrader. Note that everything goes in the internal storage of the Go and not the memory stick.