Hm, my cories are pigs. :lol: I feed mine sinking algae wafers (Hikari or Top Fin). Not sure how big yours are, but these ones, as long as they get soaked (which happens in a few seconds) drop right away.
Can you feed the top dwellers first, so they're distracted, and then drop in some wafers? You can also feed veggies like cucumbers or zucchini. IME, the top dwellers may eat some, but the cories like it a lot more. Or snail jello, they like that too.