I can't guarentee any results, but I found these lines in RMX-OS
if RMXOS::Options::REMEMBER_LOGIN
# create data stream
stream = "#{@username_window.text}\t#{@password_window.text}"
You should play around with it and try changing that last part to somehting like
stream = "#{@username_window.text}"
You might want to try it on a test game first because it might mess up your game.....
edit: I tested it and it didn't work. When I did that it didn't remember anything, so I don't think I can help you. sorry.