Honestly, I could probably create a very quick PR for Filament that would allow you to do this, however, I assume that there's no desire for that since it can't already be done
I'm trying to create a nice way to make Filament work with my multitenancy package, and because of how the package works, it doesn't need to touch Filaments multitenancy functionality
That is a mixin added to Router which does a whole host of things internally, including reading config to load and create a driver, before then asking that driver to create the route group