Reverse knockback

I asked this question somewhere else but both me and the person who answered me smacked our heads on the same wall.
In the past updates when custom enchantments came out, I remember we had the ability to create custom enchantments, which we could design to enhance knockback, but instead of having it's value positive, I had it negative. And It just worked the opposite way.
Now I haven't middled much with enchantments and I'm not sure if this was removed. But I tried replicating it and it didn't seem to work. The furthest I got is to reduce knockback more than your fist's normal knockback but that's about it. So yea I'm here to ask if this is still possible or if there's a simple alternative way.