Git allows to fetch from any given remote and reference, for example
git fetch
So that those given com
See "Pull a specific commit from a remote git repository":
With Git 2.5 (July 2015), you will be able to do:
git fetch --depth=1 $SHA1
git cat-file commit $SHA1
If the SHA1 is "reachable" from one of the branch tips of the remote repo, then you can fetch it.
Caveat: you need a Git 2.5 remote repo server though, which will handle the uploadpack.allowReachableSHA1InWant config (and you need that config to be set to true, in order to allow a single commit fetch).