How can I disable Mob (npc) fall damage?

My players are making mob farms that are destryoing the economy through the use of mob fall damage.

How can I disable mob fall damage? Is there already a plugin that does this?

edit: My economy is based of players killing mobs, not selling items.

 

NoFarm makes mobs only drop things when killed by players directly.

 

I have that installed but it does not stop fall damage.

Right now I have players making mobs fall so their on 1% hp then killing them for the economy bonus.

Well although it seems no one else has had the issue with players farming mobs after fall damage luckily the No Farm developer said he will include it in his next update

EDIT by Moderator: merged posts, please use the edit button instead of double posting.