Can I smite monsters with enemy champs on top?

This is super frustrating. You have smite ready to go on important objective like baron, only to have an enemy champion last second flash or sit on it, and have the smite hit the enemy champion. Smite should absolutely have a toggle ability to prioritize champs or monsters. Some champs with very large hitboxes make smite almost or actually impossible when they are sitting on objectives.

Any way around this I don't know about?