I thought I'd be able to track down a digitised version of the Theological Orations, but no luck so far. I don't really want to have to transcribe it, even from Migne. Nonetheless, I've made a little start. I think once I have a digitised version of the text of the 5 sermons, the process of tabulating vocabulary shouldn't be too hard (though perhaps painful). Writing some basic commentary on Greek constructions will be a much slower process, but it's often these that cause the most stumbling to readers. It's easy to check an unknown vocabulary item, but puzzling out a difficult or unfamiliar construction can stop you in your tracks.
Edit: Well, after a bit more research, I am beginning to think that I will need to type up the text myself. This will be considerable effort, but it does have some (minor) personal advantages, since I will be spending time in the text as I go and can make some notes, etc., as I type it up. Still, one would think a reasonably accessible copy of the Greek text should be available!