You can break it up any way you want to.
I'll admit that I can't currenly run 4:42 for even one mile. 2:21 for a half mile would be doable but it would likely take me several days total to get in 52+ reps of half mile repeats in that pace.
I think the best bet for me would be to break it into 400 meter repeates. Maybe occasionally change up the distance between 200 and 600 just to get something a little different.
By structuring it that way, I'm pretty sure I could finish 26.2 total miles at World Record pace in less than 24 hours.