在AutoMapper配置中，使用.ConvertUsing()方法来指定映射规则并将目标类型明确指定为实际类型，这样AutoMapper就不会将已知类实例视为Object。

代码示例：

public class Source {
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Destination {
    public int Id { get; set; }
    public string Name { get; set; }
}

// 配置AutoMapper映射规则
Mapper.Initialize(cfg => {
    cfg.CreateMap()
        .ConvertUsing(src => {
            var destination = new Destination();
            destination.Id = src.Id;
            destination.Name = src.Name;
            return destination;
        });
});

// 使用AutoMapper进行映射
var source = new Source { Id = 1, Name = "John" };
var destination = Mapper.Map(source);

Console.WriteLine(destination.GetType().ToString()); // 输出Destination