Use runner with fork without shared runner

Hi,

We have a gitlab in a company cloud. They offer a shared runner but in our project, we don't want to use it. So, I defined a specific runner well configured for our project. But when my colleague want to use it in their frok, they don't have the visibility on it. How can we do to share a runner in a group ? (we tried group runner but the visibility is restricted to a group and the forks are not in the group)