Hmmm. I don't know if you've ever seen armored cable, the armor is more like a thick foil. It's ribbed usually... and I'd bet that a rat could get through that very easily. I know you said you didn't want to, but innerduct is a great thing. Although the O.D. if your run is obviously going to increase drastically, I'd still say that's a better bet. That being said, back to your original post.. I've used berktek armored cable before, and it's just like any other armored OSP rated cable. Works well, easy to bond to a grounding clamp, etc.
I think you'd be better off using innerduct, or depending on the length of your run -- EMT or flex could be a better idea.