I do something similar but a little more manual that your solution. I `git commit -am "WIP"` to save random, odd-ball intermediate working states. Occasionally the commits get real messages but I try not to let it interrupt the flow.

Then when I'm ready to commit or cut PRs, I just squash them all down if it's trivial. If it's a bigger change: I push things to a backup branch, `git branch Branch-BK`, reset to a base commit, and use difftools to pull over the subset of changes I want and commit them repeatedly until there's no diff left.