Custom IContractResolver

public class DynamicContractResolver : DefaultContractResolver
{
    private readonly char _startingWithChar;

    public DynamicContractResolver(char startingWithChar)
    {
        _startingWithChar = startingWithChar;
    }

    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        IList<JsonProperty> properties = base.CreateProperties(type, memberSerialization);

        // only serializer properties that start with the specified character
        properties =
            properties.Where(p => p.PropertyName.StartsWith(_startingWithChar.ToString())).ToList();

        return properties;
    }
}

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public string FullName
    {
        get { return FirstName + " " + LastName; }
    }
}

Person person = new Person
{
    FirstName = "Dennis",
    LastName = "Deepwater-Diver"
};

string startingWithF = JsonConvert.SerializeObject(person, Formatting.Indented,
    new JsonSerializerSettings { ContractResolver = new DynamicContractResolver('F') });

Console.WriteLine(startingWithF);
// {
//   "FirstName": "Dennis",
//   "FullName": "Dennis Deepwater-Diver"
// }

string startingWithL = JsonConvert.SerializeObject(person, Formatting.Indented,
    new JsonSerializerSettings { ContractResolver = new DynamicContractResolver('L') });

Console.WriteLine(startingWithL);
// {
//   "LastName": "Deepwater-Diver"
// }