You can buy conduit that is very flat against the wall, and paintable if you wish, to hide the wires on the outside of the wall. Here is some with channels to separate wiring.
http://www.hometech.com/techwire/wir....html#SB-WS12T
Installing the boxes like you show is just two cuts on the sheetrock, 5 minutes. Then you fish the wires through. Couldn't be any simpler.