default resource provider and SqlResourceProviderFactory in the same asp.net application

[DesignTimeResourceProviderFactory(typeof(CustomizedResourceProviderDesignTimeFactory))]
public class CustomizedResourceProviderFactory : ResourceProviderFactory
{
    public override IResourceProvider CreateGlobalResourceProvider(string classKey)
    {
        if (classKey == "MyCustomResourceClass")
        {
            return new CustomizedResourceProvider(classKey);
        }
        else
        {
            return null;
        }
    }
    // etc.
}