Hi Jon,
You can use any gem out of that git repo that you want. For example, the rails/rails repository contains many gems, and those gems can be used without using the top-level “rails” gem. So that’s not a problem. Furthermore, you don’t have to create a git commit to be able to load your changes locally when using git locals. Have you tried git locals? It sounds like they do exactly what you want.
If you are purely debugging and don’t want to commit or push your changes, I definitely suggest using :path.