Congratulations on the hoppers taken! While snakes in the wild certainly ingest bits of unintended stuff, I do think it's best we minimize that in our captive pets.
Putting down a cardboard box lid or similar "plate" will help, but when you have a shy feeder, they want to drag it someplace "safe" to eat (where our big eyes aren't
watching them, lol). I like having some long tongs (giant tweezers & hemostats) on hand to pick of bits of substrate before a snake ingests it, but many times it just
falls off as the prey gets swallowed. Do the best you can...don't worry too much though.It might help keep your snake from feeling the need to hide while
eating if you just watch him swallow from a little further away?