It's not possible to do directly, but make a standard sprite on TOP of your TiledBG, then set opacity for this new sprite to 0 and use the sprite for collision detection.
I'm new to Construct 2 myself, and 9patch is one of the objects I haven't gotten around to play with. But as the 9patch is meant for scaling simple geometry out of aspect, without the weird things that happens as standard, I'm thinking you may be using 9patch the wrong place...? What I mean is; how about dropping 9patch and make a sprite instead? Then rotation, set angle etc. is easily solved.