A lot of my "chapters" end up with a small scene at the beginning or end -- like, at the end of chapter one, after the main characters' scene is wrapped up, there's a quick 5 page interlude of a couple of the main villains meeting elsewhere up to discuss what they've learned. I do a lot of little scenes like that; open with a short interlude, and then transition to a different scene for the main chapter, or after the main "story" of the chapter, cut away to a short interlude that gives you some clues for things to come.
I call it an "interlude," but I consider it part of the chapter! In order to avoid pacing whiplash, you don't necessarily need to say ITS THE END OF THE CHAPTER! NOW, BONUS SCENE! -- you just have to think about how you can use the pacing of your comic to show that the main scene, the main "story" of the chapter is wrapping up, and we're about to go into something a little different. I think it can be really effective to set everything up to look like the end of a chapter, have the end-of-chapter splash page or the camera pulls out like it would at the end of a scene -- and then transition or cut away or linger or zoom in on something else -- wait.... who's that sneaking off there? What's he up to?