Support for Apple App Clip in Maintenance Mode

When my site is in maintenance mode I still wish to be able to support Apple App Clips.

This requires a special META line to be added to the HTML HEADER my WP Maintenance Mode page.

I am unable to find the proper template to edit to insert the META tag in the maintenance mode page.

Is this possible? What’s the best practice for doing this so my custom META tag isn’t erased when you update your plugin?

Thanks!
scotto