Spawn points past edge of layout on unmoving layer

So, in my game, "Psi," I am wanting to randomly spawn enemies just past the edge of the layout on a layer with parallax set to 0 so they won't waste processing power by being in the layout from the beginning. Does this sound like a good idea. Can anyone explain exactly how I'd do this? Thank you.

Here's a demonstration pic of what the layout will look like:

<img src="https://dl.dropboxusercontent.com/u/60595907/Psi%20screen%201.jpg" border="0" />

You can make a sprite called "Spawner" or something, just make it a square and put outside the edge of the screen. Click on the Origin button in the sprite editor, and click the + button in the origin window to add an image origin. Call the origin point something like "spawn". Close that and add an event (System -> Every X ticks, maybe?) -> Spawner -> Spawn object at origin point "spawn".

I would recommend you set the "Spanwner" sprite to Invisible, so you only see it when you are editing your game and in no case (a bug? Who knows) the player can see it.