TypeAdapterConfig.GlobalSettings.ScanInheritedTypes(Assembly.GetExecutingAssembly());

public class InheritedDestinationModel : IMapFrom<SourceModel>
{
    public string Type { get; set; }
    public int Value { get; set; }
    public void ConfigureMapping(TypeAdapterConfig config)
    {
        config.NewConfig<SourceModel, InheritedDestinationModel>()
            .Map(dest => dest.Value, source => int.Parse(source.Value));
    }
}

public class DestinationModel : IMapFrom<SourceModel>
{
    public string Type { get; set; }
}