FYI, I made a similar request for Explorer's Compass...

Not sure if at all possible, pretty much as the title says. Is it possible to make the mod where its not also required for a client to have it installed?

In short, I'd like to be able to install the mod on the server-side, but it not being a requirement on clients, so just a vanilla client can join the server. Obviously the vanilla client will not be able to use features from the mod unless they also have it installed.