I have done it. Luckily never needed it.
Just photocopy the back of the tickets (with the #s). Take the copy with you and keep it somewhere else (in your luggage, safe, etc.).
If you should happen to lose your tickets, Guest Services can key in the ticket numbers and determine how many days and pluses are left on your tickets and issue new ones.
Not needed if you have APs. An ID is enough for them.