They can always tar up their repo and send it over. You then unpack it on your end, then set it as a remote, pushing/pulling from it as you see fit. Admittedly,

They can always tar up their repo and send it over. You then unpack it on your end, then set it as a remote, pushing/pulling from it as you see fit. Admittedly, not the greatest workflow, but it doesn't require any new tools if you are already familiar with remotes. As another alternative, git-format-patch/git-apply or git-bundle may be a quicker way of shipping changes around.