If the source and destination are mains fed, you could use a Mains Ethernet device and then connect that into a Wireless Access Point. This in effect uses the internal mains wiring to route the network to the location required and the AP to make the signal wireless again. Thinking about it you might be able to get the whole thing in one product now?
Erm Yup you can.... http://www.maplin.co.uk/devolo-200mb...xtender-397391
Vangelis