Make time/date format independent of 'locale' setting


On a European based internationally targeted forum we’re using the default ‘en’ locale to set the language to English.
Date and time presentation seems to be fixed to US format. I don’t really care about the date presentation as it is clear enough but the am/pm time presentation is not commonly used in Europe (except for the U.K.).
Unless I’ve missed something it doesn’t seem possible to set the date and time format independent of the locale setting.