Ride at a normal "I'm out for a Sunday ride" pace, not an axe-wielding race maniac pace. Do a lap have 3 hours off, repeat.
Eat. After every lap eat a small meal as soon as you can.
Sleep. Don't assume grabbing 2 hours sleep isn't worth the bother, it really is.
Get comfy. Make sure you have decent camp setup. It all depends on the weather, so plan accordingly.
Doubling up with another rider overnight will give you more time to sleep. So rather than doing riders A,B,C,D swap to A,B,A,B,C,D,C,D.
Looks at GPS tracking like http://www.mapmytracks.com or use walkie talkies/phones to avoid those 3:00AM hand-over disasters.
Concentrate on the misery of those around you to cheer yourself up!