I've have several cars including the present one, that suggests you can insert a screwdriver though the backplate, lift the ratchet away from the adjuster and zip, the drum falls off.
I have yet to have any success with this method, invariably waggling away aimlessly in space and eventually resorting to levering the drum off.
Am I missing something obvious or does it not really work in practice. I only ask now because I want the drums off again tomorrow and thought I might save myself some aggravation
Andy