On the multi button.
Left and then select single area.
Down and then the rear thumb wheel to size.
Once there if your eye is in the finder, it's a left, down, and move to point. Sometimes I'll take my eye off and use the touch screen. I usually can get it pretty close when I have an idea of the framing.
Becomes second nature pretty quickly.
Edit: I see entropicJohn over at mu43 solved it for you. Excellent.