Add function to run cron job manually

Sometimes it would be nice to be able to run a cron job manually, for example when deploying a new job that is scheduled to run every day in the middle of the night, but you want to give it an initial run when first deployed to test it out and get the effect of it running right away, rather than getting up the next morning only to discover some error in the job_run_details table.

Would it be possible to add a "run" function that would manually fire off a cron job by ID or name?