Overriding to!string on enum types

["Nordlöw" via Digitalmars-d-learn]

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.