Hmmm.
I think that it's a good idea to allow the inability to communicate to be a significant factor that may turn into violent behaviors, including not being able to "wave off" incoming aliens.
Stanislaw Lem's books were one of my favorites on a subject of first contact, with his alien species being so different you may not even understand that you're already in contact with somebody. Similarly, in Ender's Game series buggers were behaving the way they did because of lack of communication. Mostly. And it went very violent for both sides.
I personally decided to blast away any military ships that I may encounter near my colonies, despite having strong believes in peaceful co-existence.
So I'd rather have to resort to aggressive actions in order to keep the aliens away until the communications are established, instead of being able to magically sending them away.