Here's a map that's 1024 miles starting at Denver International Airport. If you are an experienced city dweller, you shouldn't have too much trouble negotiating the route across town (it's not nearly as bad as some make it out to be) You could skip the ride from Delores to Durango to cut off a few miles but Durango is about the only place in that corner of the state to rent a car if you want to go that route.

If you need to shorten the route, you might consider markf's suggestion of a shuttle to Summit County but that will only take off 70 miles or so. You could also consider going from Denver to Glenwood Springs by Amtrak and then through Aspen (I can help with the route). That would cut off about 200 miles.