You can check in on your phone at T -24 hours. You can print out later at guest services, front desk, RAC (if onsite), or at the airport.
However, this is one of the rare instances where purchasing EBCI may be worthwhile. I always hated having to additionally plan my time to make sure I can check in while at the parks. I would sometimes hang back from the family because I needed to check us in. And if we had multiple confirmation numbers, oh bother!
I'm pretty sure you can purchase EBCI just for the return leg. $12/person adds up but it can be worth it so you don't miss your child's face on Toy Story Mania.
My two cents, Steve.

B