JVM Help

Fellow geeks, I have a user with a query, and i'm having trouble finding the answer. I need a java VM switch, likely a -Duser.x that will allow one to tell a VM to use 24-Hour time format instead of defualt for English(United States), and a switch to overide the default date setting also; both to suppress the date, and to change the date format. The closest i've found so far is -Duser.timezone=GMT(+\-)n. That's fine and well, but timezone is not the issue, but rather date/time format. Suggestions?