default arguments for const ref parameters in extern C++ functions

[60rntogo]

I'm trying to use a C++ library that has a function declared like 
this:

---
struct Foo
{
   int x;
};

void fun(const Foo& foo = Foo(1));
---

I have translated this to a D declaration:

---
struct Foo
{
   int x;
}

extern(C++) void fun(const ref Foo foo = Foo(1));
---

This yields an error: "Foo(1) is not an lvalue and cannot be 
modified". I suppose this makes sense with how D references work, 
but I have no control over how the C++ function is declared. What 
can I do with this?