I think you can because I thought I did a few months ago. I think there was a drop down box where to choose which type of credit card you are using, and one of the options is disney visa, and another is disney rewards. For some reason I kept missing the disney rewards, but finally figured it out.
Whew finally got it. Had to switch to a different computer. Thanks to the second poster , I decided to click on a line that said Disney cards Disney rewards and That open up a line so I could put in the rewards number. I still couldn't get it. I opened a box that stated even if you have enough rewards to pay with your rewards card you must still enter a credit card number in case there wasn't enough money. Took me two extra days to finish. Thanks again.