Nope. People would just declare empty wars against whoever their peasants hated most so as to get the benefits.
Any mechanic that relies on player-defined diplomacy to give a bonus or penalty (aside from stuff that's specifically related to the act of fighting or supporting an ally) is likely to be highly exploitable in similar manners. Sorry.
It wouldn't necessarily be an empty war if all the peasants of Realm A hate Realm B.
