Feed 'em! I can assure you that snakes in the wild don't find "just the right size" prey for every meal.I know you're eager for him to "graduate" to larger meals, but trust me, there's no big rush.
What I'd do is keep feeding them but at slightly shortened intervals. See? You could also just save them for a little while & when he's taking larger meals, feed them 2 for one meal too. No, I wouldn't throw them away.