This is a script that adds a fully functional Fork button to your own Gist.
If a Fork button is already present in the page, this bookmarklet will set focus to it instead of adding another one.
The change is temporary and the button will disappear as soon as you navigate away from that Gist (clicking the Fork button does this for you as well). Meaning you will have to run the script every new page load.
Copy the contents from bookmarklet.js, open Scracthpad (Ctrl+F4), paste it there. Back in browser, swwitch to tab with your Gist you want to fork. Back in Scratchpad, "Run" it. Save and/or bookmark the Scratchpad file for future use.