I've settled on a workflow that reverses the situation. I simply commit all my work to the main branch and cherry pick commits into temporary feature branches only when submitting PRs.

This way I only need to worry about maintaining a single consistent lineage of commits. I've been using this workflow for about a year now and find it to be much easier than juggling and rebasing feature branches.

In case anyone's interested, I made a tool that automates this workflow. The worfklow and tool are described here: https://github.com/bjvanderweij/dflock/