AFAIK, this data will be requested at check-in. Depending on your specific visa, you can put your A-number into the secure flight information but that is as far as it goes before check-in. There is no way of entering this data earlier or even store it - every time you fly DL you have to do it again. I know, I know this is for my own protection but since I have been forced to disclose this data to DL more than a 100 times, I sincerely doubt that.