No need. Obtainium already supports downloading from third-party F-Droid, so users can add Grayjay this way:
1. Enter the URL "https://app.futo.org/fdroid/repo/"
2. In "Override Source", select "F-Droid Third-Party Repo"
3. For "App ID or Name", enter "grayjay"
4. Press "Add"
5. Done