Is it possible to to set an alternative source repo for the runner?

My gitlab-server has a large physical distance to the instances where my gitlab-runner is working.
So I want that my gitlab-runner doesn’t clone from the gitlab-server repo.
I want that the runner clones from a second repo which is closer to my runner instances.
Is it possible to set a different repo as source repo for the gitlab-runner?
I already set the CI_REPOSITORY_URL in the .gitlab-runner.yml file.
But it doesn’t seem to have any effect.
Is there a way to change the source repo?