We were in the same position (although luckily far fewer repos than you!). It took a bit of fiddling, but in the end I found that it was actually quite easy to

We were in the same position (although luckily far fewer repos than you!). It took a bit of fiddling, but in the end I found that it was actually quite easy to fix this by tacking on a force push to the main branch of the heroku git repo at the end of our existing CI process (essentially treating heroku got as a deploy api that happens to use the git protocol) Don’t blame you for wanting to move, but you might find that approach helpful as a quick fix.