I typically use (and others) git commit --fixup=... which creates new commit. Then you can do git rebase -i --autosquash origin/master and it will automatically squash all such commits.

Since it's best way to not force-push into pull-requests, would be nice to implement this feature.

P.S. more examples at https://fle.github.io/git-tip-keep-your-branch-clean-with-fixup-and-autosquash.html