"cycling rigors of a 5-day tour"

does this mean you've got a set number of miles you have to do in those five days? It's pretty basic. If your five days average out to 50miles a day then hopefully you've experienced a 75mile day, or sequential 50mile days. If your trip involves sequential 75 mile days then hopefully you've experienced sequential 75 mile days or a 100 mile day with 25mile days on either side.

If you cannot do that before the trip then the trip is just another training ride where you have to have time to recover each day and ride the next day. Which means taking it EASY and simply sitting on the bike a long time and getting off frequently so you don't develop overuse injuries like saddle sores, dehydration, bonking and bad attitude.