This is the forum I promised I'd make for LB!
I'm going to expand on his JUMP example!
I am now working with him to make random levels!
I have done this, LB:
You can use an active object that you create backdrops from so you don't have to change the code much. You'd need to remove the existing backdrops and make the frame virtual width -1, and remove the victory/goal conditions.
Exactly as you asked. Well, you did ask for the active backdrop thingy, so what I did, is I (Just as a test, so you could see) let the player ride the actives created when you jump and hold!
Take a look:

