Instead of trying to fill that small gap with T&G, I decided I'd cover it up with a piece of rough sawn Douglas Fir. I was able to press this into the uneven stucco a bit and the painter would be able to caulk the seam and make it much cleaner. The alternative of try to scribe the T&G to the house would have taken way too much time. I did the same on the other side of the addition.