git add-archive <sha>

.gitconfig

[alias]
  add-archive = "!runit() { REFS_BRANCH=`git branch -a --contains $1 | xargs` && \
                 NEW_REF=`echo refs/archive/$(date '+%Y-%m-%d')/$(git config user.name)/$REFS_BRANCH/$(date '+%s')` && \
                 git update-ref $NEW_REF $1 && \
                 echo consider deleting $REFS_BRANCH && \
                 echo attempting to backup archives && \
                 git push origin refs/archive/*:refs/archive/* && \
                 echo Here is your remote commit ref url && \
                 echo https://github.com/org/repo/commit/$1; }; runit"

git branch command may need --format=refname, or something similar, to remove prefixes like + and *.