If you ever want to ignore a file from git, but don't want to add it to the .gitignore file, you can do it on your local copy by adding it to the file ".git/info/exclude"
I've setup an alias to do so, just add this to your .gitconfig file under the [alias] section
exclude = !sh -c 'echo "$1" >> .git/info/exclude' -
Then you can execute:
git exclude SOME_FILE