Essentially, I want to merge a feature branch into main when the two branches have diverged and I can’t fast-forward the merge.

If doing this manually, I would checkout the feature branch, rebase it onto main, switch back and merge the result. This, however, changes the feature branch, changes the working directory unnecessarily, and is just a little too much work for what is a straightforward option on GitHub.

What would be a good and safe way to do git rebase-and-merge without these drawbacks?