I don't think having avatars on the site will need GD. I imagine your upload script uses GD to
1) make sure it's a real image file
2) make sure it's the right size
3) (maybe) convert the image to a standard format (ie jpeg), but probably not.
If you know these things already, you can bypass using GD right now by uploading the avatars using FTP or CPanel into the directory (probably called "avatars") where you have your avatars.