Great question! As Frazzle mentioned, I did move out of CP housing about 2 months into the program. My understanding of the rules is that the only way to not live in the housing is to move in with an immediate family member (spouse, parent, etc.)
I moved in with my husband and had to get an official certified copy of my marriage license (that they could keep for my record) and had to go through a couple of different people in the housing office to get it finally approved. There is an appeal board, so if you make a good enough case the board could approve you living off-site.
Here's another thing, you do not have to physically stay in the housing, so you could always get a place and just pay your CP rent - which is no fun. Towards the end of your program you could start looking for housing then just move out a couple weeks earlier so that you would not have to pay as much in the CP rent.
I will tell you that being a Disney employee has it's perks, I get a discount at my current apartment because I work at Disney. If you get a place before you start then you wouldn't be able to get as good of a deal - just another thing to think about!