While looking at the Gtkmm to see how they generate a C++ binding for Gtk, I found that Scheme is heavily used, in order to generate classes, enums, etc. automatically. Not sure if it's feasible or not here, or if there's a better way of doing so, but the idea is good to look at.
An idea could be to create a tool to make this more smart and even generalized, so it looks for everything in the library and make the relation automatically. In this case, we can have more FFI things with the development being quick and easy. However, it's just an idea, it may be hard to implement.