json.net: specify converter for dictionary keys

I have a JSON:

{ 
    "data": { "A": 5, "B": 6 }, 
    "foo": "foo", 
    "bar": "bar" 
}

I need to deserialize data into a class:

public Dictionary<MyEnum, int> Data { get; set; }
public string Foo { get; set; }
public string Bar { get; set; }

But MyEnum values are CodeA, and CodeB instead of simply A and B respectively.

I have a custom Converter that can handle conversion. But how do I specify a JsonConverter to use with Dictionary keys?