I am seriously thinking about taking on this challenge...
CTS Bucket List Challenge
Sixteen teams of the world's best cyclists are getting ready to take on the thin mountain air from August 20-26 for this summer's major stage race in Colorado. They will have to ride 683 miles in 7 days to complete the race, and if you can ride the same distance - 683 miles total - between August 20 and August 26, you'll earn your Finisher's badge and commemorative patch in addition to some serious bragging rights. Get all of the details and join the challenge here.
You might check with Adam S, Abby S, Holli F, Kim G, Jason B, Scott A, et al who just did a tough multi-day CO tour in altitude, with attitude, for tips and hints.