If you have a loose substrate, like aspen, there are 2 things you can do. One, is feed him outside the enclosure with isn't recommended because it can stress out the snake and turn off feeding. However sometimes you have to, like with mine, he won't eat unless you dangle a F/K in front of him and the only safe way to do so is in a shallower feeding bin. The second alternative is to put parchment paper or newspaper down under the mouse. I do this for my boa. This prevents the snake from ingesting any pieces which can cause impaction.

Secondly, how big is your snake? It is very hard to rely on petco for advice. They told me I should be feeding my 28" ball one pinky or hopper a week. This is WAY underfeeding.