Perhaps you could add a modifier that allows you to attach an elytra to the chestplate.

Sorry, but the logic is hardcoded for the elytra flight checks and I don't want to do any coremodding in this mod. I'll look into it again if Forge accepts my pull request for the elytra flight attribute or if some other update happens.

This was/is being worked on here

@Pirateboy04
That one was closed for inactivity, mine is a more recent and currently updated one that is based off the same PR: MinecraftForge/MinecraftForge#4958