1. Switch to a new branch
2. Commit the changes
3. Revert the changes
4. Merge the branch into master, as `--no-ff`

The result will be this history:

 ... A ── B ──────────── C ── D ... ─master
 ╲ ╱
 idea ── undo ─experiment

Advantages:

- The addition and deletion are clearly grouped together, and can still easily be referenced.
- There is a continuous history skipping the whole experiment, with an empty diff between `B` and `C`.
- There are no unmerged branches to be kept around. The `experiment` branch can be deleted without losing the commits.