[Fallen]

I used to have the same bad habit as you. I forced myself to stop by gluing on those long fake fingernails that girls like to buy. It feels weird biting them, plus I spent money on it, so eventually it made me stop. Maybe the same will help for you?

Sadly, however, that lead to me biting the skin around my nails. xD
Currently have not found a way to break this habit.