Is your relationship with this person still contentious? I think there is something fun about keeping an "enemy" on their toes, which being magnanimous and giving towards them surely will. Unless they are completely horrible, they will likely re-think some of the more horrible thoughts they have had for you and maybe that stretch us unease they feel will make you happy to think about. Just as an example, I've sometimes wanted to donate money to a raging leftist on reddit who is posting in one of the help forums and then PM them to let them know I'm a Trump supporter.