I don't think you can pay days ahead of time without the dining plan.
You can however ask for your bill when you sit down at a buffet. I do that so we can leave right after we see the characters without waiting for our bill.
And you can cancel reservations that aren't prepaid or guaranteed by a credit card ahead of time anytime you want. Or just not show up (but thats not cool).
is the only character meal that is prepaid. The dinner shows are also prepaid. Disney asks for a credit card number for some other restaurants to charge a no show fee but you have to settle up at the restaurant.