In theory, you could use one layer for the terrain and one layer for the background. When you need to destroy terrain, you would paste a transparent color to the background of the terrain layer. Haven't tried it though.
As a matter of fact, it has.
http://www.bumderland.com/objects/
A long with a bunch of other extensions. I think the list of converted extensions is filling faster then I thought.
Edit: Kirby Smith: If you were to apply a transparent color over a backdrop, how would that mask the collision, and make the actual pixels of the backdrop actually disappear for you to see behind them?
I tried active overlay, and you can do player collides with overlay -> stop. But it doesn't seem to do anything.
There must be a way to do this, but if not, you could possibly make a terrain out of a backdrop aswell on another layer, but hide it, and use that as a background..
The active overlay just reads the adress of a normal overlay... You have to make the source overlay transparent background...
Also make sure you have Overlay Redux