If there's enough size disparity (and the hermit isn't starving) then you can probably keep some smaller snails with him. Try to find the smallest Cerith snails you can - sometimes you'll find them as small as 1/4"-1/2", which would be perfect. (Hermits at this size are great too....sadly they all grow into omnivorous monsters...LOL.) Empty shells don't seem to be very attractive, but regardless do make sure to have a couple empty "upgrade" shells in the tank for him to use as he grows.
-Matt
-Matt