(There was already basically the same question "create a git symbolic ref in remote repository", which received no universal answer.)
But there are a specific answers for various git "farms" (where multiple users can manage git repos through a restricted interface: via http and ssh): http://Github.com, http://Gitorious.org, http://repo.or.cz, Girar (http://git.altlinux.org).
These specific answers might be useful for those reading this page and thinking about these specific services.
$ ssh git.alt help | fgrep branch
default-branch <path to git repository> [<branch>]
$
for example ssh git.alt default-branch packages/autosshd.git sisyphus
to change the HEAD in the remote repo autosshd.git
to point to the sisyphus
branch.