Necessity is the mother of invention. I sleep 3-4 hours most days and then periodically sleep for 8 hours one day. One thing that most people who have a record for sleeping only 4 hours or so at night is they nap during the day. When they have 30 to 45 minutes of free time in the afternoon, they nap in their chairs.
An alternative is to meditate 30 to 45 minutes in the afternoon. I cannot guarantee that it will help you to sleep less at night but many meditators find they need less night sleep.
Alex
