Marshaling an array as a return value?

How do you marshal an array as a return value   What marshalling attributes must be specified

Specifically, using COM Interop, I want to use an interface member that returns an array.  The implementation of this interface is written using an unmanaged object and a COM style interface.

In C#, the interface declaration would look like this:

    public interface IMyInterface
    {
        int[] MyArray
        {
            get;
        }
    }

In unmanaged COM interface land, the property get function looks like this:

    struct IMyInterface : public IUnknown
    {
        virtual HRESULT STDMETHODCALLTYPE get_MyArray( int** array, int* size );
       
        // array is an "out" parameter, a pointer to an array of integers
        // size is an "out" parameter, and returns the number of elements in the array.
    };

How do I provide marshalling attributes on the MyArray property get declaration such that I can call this function

If it's not directly possible, then I am willing to make some compromises:

1)  I'm prepared to accept a method declaration in the c# interface declaration, rather than a property get.  Like this:
   int[] MyArray();

2)  I'm prepared to rewrite the implementation of the get_MyArray unmanaged function

3)  I'm prepared to modify the signature of the unmanaged function.  For example, I'm okay if it has to look like this:
    virtual HRESULT STDMETHODCALLTYPE get_MyArray( int* size, SOMETHING<SOMETHINGELSE>* array );

3)  I'm prepared to allocate the array in the implementation using CoTaskMemAlloc or whatever memory allocation necessary.

Some details on which I am NOT willing to compromise:
1)  The array must be a return value in C#.  I am NOT prepared to change the IMyInterface method to this:
    void MyArray( out int[] array, out int size );

2)  I do not want to take additional marshalling steps in the caller.  So I don't want to have to call:
    Marshal.FreeCoTaskMem()

3)  The size of the array must be variable, in that it must not a constant size in the marshalling attributes.  The returned array, could contain any number of elements.
   

Here's something I tried that did not work:

    public interface IMyInterface
    {
        int[] MyArray
        {
            [ return : MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1) ]
            get;
        }
    }

I get the following error:

    An unhandled exception of type 'System.Runtime.InteropServices.MarshalDirectiveException' occurred in Test.exe

    Additional information: Can not marshal return value.