Shared runner - customise run command

Hello there.

I am using a Gitlab CI / CD shared runner. I want to customise the docker run command on which the base image (specified in the .gitlab-ci.yml) is spun up from the shared runner.

For context, I would like to add -v /var/run/docker.sock:/var/run/docker.sock to the run command.

Is this possible when using a shared runner?