If you cant get into the walls, you really only have a couple of options:
wireless: if the item you are working with can do it.
drywall/carpet padding/baseboards: this is risky. I have seen some that is very good, and others that looked like speed bumps in the road. Running a dado in the backside of a baseboard is the best way. You go into the wall high and out low where the baseboard is. This requires that you pull long lengths of it off. It can be made to look very good. If you royally screw it up, you can replace baseboard.