Can you think of anything the delegates could have done to ensure the ratification of the Constitution without perpetuating the institution of slavery?

There wasn't much that could be done. Slavery was integral for everyone because slaves built the economy into what it became. Even northern states had slaves before they freed them. The only thing that they could've done is try to have people vote whether or not they want slavery, and even then many states would've had the population support slavery like it happened years later.