Best practice for cocktail with an application loading dynamic XAP

Hi, 
I try to implement some of the Cocktail's concept in my application but I don't really know what is the best way to do it.

I have an application which dynamically load its modules (XAP). Each module consist of 3 assemblies (one for the model, one for the screens/viewmodels and the last one for the repository stufff).

- Is having the EntityManagerProviders/SampleDataProvider in the Silverlight Model assembly a good practice (this is actually where I put them) ?
- The application does know about the existance of the EntityManagerProvider only after the one of those XAP is loaded. So where (and how) can I put the lookuprepository initialization ?
- Same problem for the ISampleDataProvider ...

I tried differents ways but none looks very good. 
Maybe have a class dedicated to Initialization which could be triggered right after a XAP is loaded ? but how to get an instance of it thru MEF since the main application doesn't know the type of T ?

I was thinking of something like this :

[Export]
public class InitializeModel<T>
{
  [ImportMany]
  public IEnumerable<IEntityManagerProvider<T>> entityManagerProvider;

  [ImportMany]
    public IEnumerable<IDataSampleProvider<T>> dataSampleProvider;

   public INotifyCompleted Initialize(){};

}

What is for you the best practice for this kind of problem ?

Regards,