You should be able to type it with the letters. (I've had this question a few times now. I will add it to the FAQ soon)Thanks mostthe3rd for the offer. Sadly I have yet to see a ditto in my AS playthrough so I can't put it on GTS as a desired pokemon. Being frustrated at the moment by the mirage islands. Once I see a Ditto I'll let you know.
(Someone correct me if I'm wrong.)