Help! How to prevent off hand from using items!

I'm trying to make a new seed item that can be used to breed chickens. However, for whatever reason vanilla breeding items for chickens will always take priority over my custom one even if the vanilla item is in the offhand! Is there a way to fix this or a plugin that can correct this? Also, it's annoying that there isn't an event trigger the checks if right click on entity with offhand.