I'd do as Craig suggested...a cardboard box lid makes a good plate, or a plastic top...even a real plate. A little substrate ingested is not usually an issue, but a
little bit each time could build up into something the snake can't digest or pass...remote chance but these are our pet-pals, & the problem is easy to avoid.
The problem with a paper towel is that moisture makes it stick to the prey & get swallowed; never use paper or cloth as a "plate". Good question.