So in the past 8 days he has averaged 47.5 miles per day. If you walk 15min/mi pace for 12 hours per day, while still getting 8 hours of sleep per night, which is 48 miles per day. Anything under 50 miles per day, I think anybody could do with about 3 weeks of long walking training beforehand. Possible schedule for 48 mi/day walking 15min/mi pace:
7:30am- Wake up, eat, prepare
8:00am- Start walking
12:00pm- Lunch, recover
5:00pm- Dinner, recover
10:00pm- second dinner, clean up, post on letsrun
This schedule gives 4hours for eating and other stuff, 8 hours of sleep, 12 hours of walking. 48 miles per day is not insanely difficult.