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 "" being one of the latest commit in the repo, as shown by https://api.github.com/repos///git/refs/heads).
===
URL : https://api.github.com/repos///git/refs
POST BODY : { "ref": "refs/heads/test", "sha": "" }