Overriding to!string on enum types

[Nordlöw]

Is it possible to override the behaviour of to!string(x) when x 
is an enum. I'm asking because this

enum CxxRefQualifier
{
    none,
    normalRef,
    rvalueRef
}
string toString(CxxRefQualifier refQ) @safe pure nothrow
{
    final switch (refQ)
    {
        case CxxRefQualifier.none: return "";
        case CxxRefQualifier.normalRef: return "&";
        case CxxRefQualifier.rvalueRef: return "&&";
    }
}

doesn't affect behaviour of to!string(x) when x is an instance of 
CxxRefQualifier.