One idea might be to speak to a home security/burglar alarm company. I've had alarms retro-fitted to a couple of houses in the UK and both times the installers were very creative in routing the cables almost invisibly. (There were inevitably one or two stretches that could not be hidden).

If you have to run cables over the surface of the walls, can you box them in and redecorate the boxwork? Can you run the horizontal cables through coving around the edges of the ceilings?