up arrow<p>ctrl-a (readline command for beginning of line)<p>type "sudo"<p>Also, ctrl-w is really useful. Heck, learning the readline editing keyboard in general is really useful.
Most often case is when you forget to type sudo before command. This implementation propose to re-type executable name in all-caps (or type it in all-caps beforehand).<p>More efficient approach is to use keybinding like Ctrl+T to prepend sudo to the current command (or to the previous command if current is empty).