Instead, you're just going to have to ask for it according to their Facebook and Twitter accounts (they're going with the hashtag #AskForTheSauce).
According to customer comments/complaints posted to those same accounts, they might have jumped the gun on the announcement as at least some locations haven't yet received the sauce (I checked my local Burger King and they had it though).
Apparently, it tastes like a combination of barbecue sauce and honey mustard, which begs a comparison to Chick-fil-A sauce.
There's no word yet on whether the sauce is for a limited-time only or permanent.