You can't define what font to use for specific screen/element and you can't load new fonts using interface .ini files only. Even if you'll change scripts to load new fonts, it would be pointless becouse of the first problem. You're stuck with replacing files only; remember that client does not load everything in fonts/ - it looks for specific files~
I'd go with removing worldmap clock - if it doesn't ruin whole concept - so you don't have to worry about it. It's not a must-have after all, and player can always press "/" to get ingame time.