Thanks for discovering the features in the comics engine.
In the meantime, I'll settle for manually setting fit-content-width and landscape orientation for each pdf file I open. For the sake of other users with the same desire, the keyboard shortcuts are:
Shift S (fit content width, cropping margins)
Shift K (rotate 90 degrees counterclockwise)
(For each operation, press the Kindle keys one at a time, not simultaneously.)