Themeing Maintenance Mode in 8.2.1

Permalink August 08, 2017 at 9:40 AM

I am trying to get maintenance mode themed in 8.2.1 from a packaged theme

Config::save('app.theme_paths', [
            '/register' => 'my_theme',
            '/login' => 'my_theme',
            //'/maintenance_mode' => 'my_theme', // old url (a)
            //'/frontend/maintenance_mode' => 'my_theme', // new url, but core bug if this is used (b)
            ]

/login and /register work as usual.

uncommenting (a) has no effect.
uncommenting (b) results in a core code error.

Any tips on themeing maintenance mode?