gistfile1.cs

public class SomeService
{
  public string GetValues()
  {
    return "huzzah";
  }
}

public class Person
{
  public virtual long Id { get; set; }
  public virtual DateTime CobDate { get; set; }

  readonly SomeService someService = Mixin.Mark<SomeService>();

  public virtual string GetSomeValues()
  {
    return someService.GetValues();
  }
}

public class Mixin
{
  /// <summary>
  /// Mark a field as a mixin target
  /// </summary>
  public static T Mark<T>()
  {
    var proxyFactory = new ProxyFactory();

    return proxyFactory.CreateProxy<T>(new MixinWrapper(), typeof(IMixin));
  }

  /// <summary>
  /// Hydrate any mixin fields with an actual instance. Mixin fields are determined by:
  ///   * Being of a type that implements IMixin
  ///   * Having a value of Mixin.Mark();
  /// </summary>
  public static void Hydrate<T>(T instance)
  {
    var mixinTargets = typeof(T).GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)
      .Select(x => new { field = x, mixinType = x.FieldType, currentValue = x.GetValue(instance) })
      .Where(x => typeof(IMixin).IsAssignableFrom(x.currentValue.GetType()) || typeof(IMixin).IsAssignableFrom(x.field.FieldType));

    foreach (var target in mixinTargets)
    {
      var mixinInstance = Activator.CreateInstance(target.mixinType); // YOUR CONTAINER HERE!

      target.field.SetValue(instance, mixinInstance);
    }
  }

  private class MixinWrapper : IInvokeWrapper
  {
    public void BeforeInvoke(InvocationInfo info)
    { }

    public object DoInvoke(InvocationInfo info)
    {
      throw new UninjectedMixinException();
    }

    public void AfterInvoke(InvocationInfo info, object returnValue)
    { }
  }
}

public class UninjectedMixinException : Exception
{
}

public interface IMixin
{}

Random idea for mixins. Not sure this is any better than constructor injection, but it certainly is clever ;)

Usage:

In your entity:

MyService someService = Mixin.Mark<MyService>();

or
MyService someServiceThatImplementsIMixin;

After fetching/creating your entity (probably do-able using an NH interceptor):

Mixin.Hydrate(my_entity);

Ta-da, your mixin fields have values!