Bumping this - because it's 2019, and this still hasn't been implemented.
I would suggest anyone wanting this feature submit it via Garmin's "Share Ideas" page:
https://www.garmin.com/en-US/forms/ideas/
Not only that, but I would also love to have running pacing displayed on mins/mi, mins/km but also sec/200m, sec/400m or sec/800m all at the same time for track workouts! I know you can add a CIQ field for those but you can only have 2 of them ... how stupid is that?!?