Well, it's a bit of a memory waste, but you could have all of the possible tiled backgrounds in place, generate a random integer, then destroy every background that doesn't correspond to it.
Alternately, using sprites, there's having one object with several frames of animation, and using that random integer to pick which frame; but I'm guessing that's pretty similar to what you were trying.
Pardon the vague-ish answers but it's hard to know exactly what you're trying for without more detail. Good luck!