Menu bar clock does not respect custom date format

I'm still running the last version of Mojave (need some 32-bit apps). When I opt for the menu bar clock to display the date in Date & Time Preferences, it will only use the default format of the region selected in Language & Region Preferences. Custom formats in L&R do not work. Is there another way to get it to display the way I want it to? Is this fixed in Catalina?

I tried copy-pasting the date elements into the time display formats, but it didn't do anything.