You can buy online with DVC and/or AP discounts. You just have to be signed in with your AP or DVC membership properly tied to your account. I did this no problem. No need to call. Got the discount.
Keep checking back. They may increase capacity on some of these, depending on their comfort level of how things go. I saw a news story a few days (maybe a week) ago about how some "sold out" dates for boo bash had availability again.
I saw mention on the main Boo Bash thread that people are cancelling their trips and getting refunds for their Boo Bash tickets. That would open up some availability too, especially in the near term.