I've thought about this as well... here are some examples of Introverted uses of Extraverted functions:
Fe: Contemplating social rules, etiquette, political views, attachments to people, the kind of "message" you want to send... in isolation. Possibly regarding theoretical people, past situations, projections of future situations, or even the characters in a book you're writing at the moment. Okay, this one is a bit of a leap... Fe is the most dependent on and related to actual people of all the Extraverted functions. This forum might be the odd exception, because I can interact with people without actually having to deal with them in real time, and there's definitely a lot of Fe stimulation here. Writing letters to people might be an older example.
Te: Thinking of ways to apply existing systems to accomplish something efficiently/effectively. This could be used with just machines rather than people, obviously. It could even be done completely in the mind with theoretical situations or examinations of past situations.
Se: This one is the most obvious. You can get drunk, enjoy your food, listen to music, or dance alone.
Ne: The Internet, anyone? You can use Google, read books, get ideas from television, etc. There are plenty of ways to get ideas about reality without people being involved.