You could go to gifworks.com and add 10 white pixels to each side.
It doesn't appear to give me that option. It has a resize option but no "enlarge canvas" or "add borders" options that I can find.
Grrr... I'll have to dig up the tools that I used to originally make it. I had a tool that turns a flash animation into an AVI. Then I used a different tool to convert the AVI into an animated GIF. Then after much optimization to reduce the color depth, I ended up with what you see here.
For a custom avatar, the forum should just let you have whatever size avatar you want as long as it's 120x120 or less, rather than scaling everything up to 120x120.