Possible to create Graal native function callable from C without isolate?

I'd like to create a library, written in Java, callable from C, with simple method signatures:

int addThree(int in) {
  return in + 3;
}

I know it's possible to do this with GraalVM if you do a little dance and create an Isolate in your C program and pass it in as the first parameter in every function call. There is good sample code here.

The problem is that the system I'm writing for, Postgres, can load C libraries and call functions in them, but I would have to create a wrapper function in C that would wrap every function I wanted to expose. This really limits the value of being able to slap something together in Java and use it in Postgres directly. I'd have to do something like this:

int myPublicAddThreeFunction(int in) {
  graal_isolatethread_t *thread = NULL;
  if (graal_create_isolate(NULL, NULL, &thread) != 0) {
    fprintf(stderr, "error on isolate creation or attach\n");
    return 1;
  }
  return SomeClassName_addThree_big_random_string_here(thread, in);
}

Is there a way, in Java alone, to expose a simple C function? I'm thinking I could create the isolate in a static method that gets loaded once on startup, somehow set it as the current isolate, and have the Java method just use it. Haven't been able to figure it out, though.

Also, it would be real nice not to have to append a big random string to every function name.