Raise an interface's event in an extension method

[SLH]

I want to implement my own messaging system, and as part of that i've got the interface and extension method below defined:

public interface IMessage<TArgs> where TArgs : EventArgs
    {
        event EventHandler<TArgs> Fired;

        object Sender { get; set; }
        TArgs Args { get; set; }
        void Dispatch();
    }

    public static class MessageExtensionMethods
    {
        public static void Dispatch(this IMessage<EventArgs> Message)
        {
            if (Message.Fired != null)
                Message.Fired.Invoke(Message.Sender, Message.Args);
        }
    }

Trouble is, i get an error:

The event 'XNAEngine.Messaging.IMessage<System.EventArgs>.Fired' can only appear on the left hand side of += or -=

This error makes sense, however i want to raise the event in the extension method of the interface so i don't need an identical method in each class.

Any ideas? I've tried searching, but all i end up with is general info about extension methods.