ride it so fast you don't have to sleep. Okay, might not be realistic.
I assume that the format will be 400k, overnight, 200k. Have a drop bag ready with everything you need for the second day. I am paranoid and keep the second day's cue sheet on the bike. But it's a separate cue sheet. Organize clothing so that everything is in a 5 gallon ziplock bag. Anything that you might not need shouldn't be in that bag. Also organize it so that you have any food items easy to put on the bike. It's very easy to waste a lot of time getting ready.
Arrange to be woken up at the end of a 90 minute sleep cycle. Depending on how easily you go to sleep, you will want to add 10 minutes or so. So tell them 100 minutes, 3 hours 10 minutes, etc. Make sure they know not to wake you early. Probably want to set an alarm too. That can be a big deal if you are off. Sleep is a big subject. The main thing is to not worry about getting to sleep, it will happen