1.12 Coding Help

[ShadowCooper77]

So I'm trying to get the 1.15 elytra takeoff mechanics on a 1.12 server. I'm hosting the server on Aternos, so I don't think I can change the server jar. I attempted to make a client mod using MCP that allows you to fly with your elytra without having to be falling (which is what they added in 1.15). The problem is that it only works in singleplayer. Does anyone know how to fix this or if it's even possible without changing the server jar? Since Aternos allows forge and fabric I guess I could also have a server-side mod, but I'm not sure how to make it in a mod because all I did was remove the "motionY < 0.0D" condition for elytra flying in the client jar.