You have several options. If you have a mobile phone that is web enabled you can use
http://mobile.southwest.com, you can have someone at home check in for you, guest relations at all parks will check you in (they may not print out boarding passes though), as well as the hotels. Keep in mind that you do not need to necessarily print out the boarding passes as you can get those printed, or reprinted, at the airport. You just want to make sure to check in. Good luck.