How to instantiate a MonoBehaviour from a downloaded DLL at runtime?

Hello,

Is it possible to download a DLL at runtime and instantiate a MonoBehaviour subclass in it? If yes, how?

The MonoBehaviour subclass is like this:

   public class TestScript : MonoBehaviour {
       ...
   }

I put the dll under Application.persistentDataPath, and tried:

   GameObject go = new GameObject();
   MonoBehaviour mb1 = go.AddComponent("TestScript") as MonoBehaviour;
   MonoBehaviour mb2 = go.AddComponent(Application.persistentDataPath + "/TestScript") as MonoBehaviour;

but both mb1 and mb2 are failed with error:

Can't add component because class '...' doesn't exist!

I searched here and found:

http://answers.unity3d.com/questions/30143/how-can-i-put-components-in-external-dlls-and-stor.html

seems Unity3.5 does support to access component in a DLL, but how?

Thank you