On http://hurl.it/ using HTTP basic AUTH and the inputs below you can create a branch on github without having access to a local git repo.
(With "<SHA-TO-BRANCH-FROM>
" being one of the latest commit in the repo,
as shown by https://api.github.com/repos/<AUTHOR>/<REPO>/git/refs/heads
).
===
URL : https://api.github.com/repos/<AUTHOR>/<REPO>/git/refs
POST BODY :
{
"ref": "refs/heads/new-branch-name",
"sha": "<SHA-TO-BRANCH-FROM>"
}