My method is a bit more difficult to master, but it provides for a very solid attachment to the wall without touching the outside frames that you can see from the front.
Attached is a picture which shows my mounting method (sorry about the quality of the Paint picture). Basically you attach two pieces of wood to the frame that have a angle cut from them. One half of the angled cut attaches to the wall and the other half is attached to the frame.
The most difficult part is back-figuring exactly where to mount the wood to the wall so that when you put the screen on there, it lies where you need it to. I am lucky in that I can tilt my PJ up/down a little to compensate if it isn't exactly lined up.
If you need further clarification, let me know.