In a previous life, I worked for a security company (before everything was wireless). It is ALWAYS possible to hide a wire. Here are some options:
1) Baseboard- You can pull the base board and cut a notch in the back to staple the wire to. The re-install baseboard and be careful where you put the nails.
b. Get some 1/4 round or shoe molding. Notch the back corner of it on table saw. Lay the wire down where the baseboard meets the floor, and install molding over it. care with nails again.
2) Crown molding- Same idea, but a little more difficult since the run up the wall to get to the ceiling is more difficult to hide.
3) A/C ducts. You have to use plenum rated wire! All of your duct work connects to all of your rooms. This way is REALLY difficult, and it doesn't help in hiding the wire once it comes out of the duct. If you have floor ducts, this can look pretty decent. I've seen people tie fish string (not fishing line, but string meant specifically for pulling wire) to duct cleaning tools, RC cars with a camera attached, and even a trained rat! (The guy with the rat was eff'ing awesome!)
Just a couple of tricks of the trade for getting from room to room. We used closets a lot. Hide a wire in a closet along the corner behind the door. No one looks there. Doorways: If you are going to use the baseboard technique, you will need to get around door jambs to get from one room to another. Drill a hole through the wall where the baseboard meets the door casing, but don't try to go straight to where you want it to pop out on the other side. You will either miss and be in the middle of the wall on the other side, or catch the edge of the casing and split it on the other side. Drill from both sides at the same angle toward the door. About a 20 degree angle works well. Drill about half way through, and do the same on the other side. The goal is for the two holes to intersect, but not at such a sharp angle that the wire won't make the turn when shoving it through.
My favorite way to do it was to pull the base board, but everyone had their own way.