It is possible… sort of…
One could create a Discourse Connect mechanism (well, any mechanism really) that automatically logged in users to a random (new) account every time they hit it.
If you want a mix of “throwaway” and “real” accounts, that mechanism would need to allow them to select between. Or, you might use one mechanism for “throwaway” and another for real users.
From Discourse’s point of view, it’s not really anonymous posting, but considering the entire system in place it would be.