You are an admin.
Hear me out:
When a Pokemon name is typed in that is invalid (a.k.a. typing Cheeseburger in the name slot), instead of making it completely unusable, make it so that its type and base stats can be edited, it can learn any ability and move, and is only usable in Custom Games.
Therefore, you can add fanmades and new Pokemon to Showdown and make them playable without having to dig through the GitHub.