Anything you tried in the parks would be a very high risk, even in an out of the way area. Disney is very protective of it's weddings and if they suspected, or you were caught, you would be unceremoniously escorted off the property. You may be lucky and pull something off around the resorts, but it still carries the risk that you would be in trouble if a cast member saw you or someone suspected what you were up to and reported it. I can't imagine having your wedding interrupted and being dragged away would be a particularly romantic memory...
Couples save up and pay a lot for their Disney weddings, so it's also not a question that will win a lot of points here, as you are basically trying to get for free what other people pay a lot for.
Now, all that said, if you were to have a private ceremony in your hotel room, no one could stop you. There was a couple that posted a few years back about a small wedding they had on their hotel room balcony. So maybe look for a hotel room with a great view and then go celebrate in the parks?