I have tried to tackle this problem of getting access to Fmod in another way - by adding the available wrapper classes you get when you download the api engine and building some code around that. That way I have gotten a little further.
Please check it out:
Perhaps the solution can be found there - at least for us that are willing to use C# to get access to Fmod.
I understand I am not alone wanting to get access to Fmod in Godot. This could be a solution.