Then you'd need to modify the C/C++ code so that it doesn't return a Widget type or whatever and instead serializes the data in such a way that it can be deserialized by the caller.

At this point it's just FFI with me doing all the work. Plus, every time a function is called with different arguments, the C compiler is invoked (this also means whoever is running the code will need a C compiler installed, which seems like a big ask).