It also helps if you don't view it as training. Like the DD, you're riding should be relaxed. Ride out to a pub, sit down and have a meal, and a pint if you fancy, ride home a slightly different way. What would have been a hard 40+ mile training ride becomes a 60+ mile day out. You'll be tired at the end but you won't be knocked out for the next day when you should go out for a least a short jaunt, if for no other reason than to loosen up stiff muscles. After that its only another 40-50 miles for the DD, and they come pretty easy at night, even though it'll seem hard at the time.
It also helps if you don't view it as training. Like the DD, you're riding should be relaxed. Ride out to a pub, sit down and have a meal, and a pint if you fancy, ride home a slightly different way. What would have been a hard 40+ mile training ride becomes a 60+ mile day out. You'll be tired at the end but you won't be knocked out for the next day when you should go out for a least a short jaunt, if for no other reason than to loosen up stiff muscles. After that its only another 40-50 miles for the DD, and they come pretty easy at night, even though it'll seem hard at the time.