It seems that the Wii Sensor Bar runs on 7.5 volts barreling out of the Wii console itself. Therefore, an industrious young man, if he put his mind to it, could add a DC adapter from Radio Shack. That’s just what the folks at AVSForums did, with mixed results.
The problem is that the cable connected to the sensor bar is very thin and difficult to solder. Not impossible, mind you, but difficult. It looks like the best bet is to crack open the sensor bar itself and run a new DC cable. Anyway, the discussion is fairly heated, if elementary.
There’s also this little ditty that lets you create a fully functional bar that might be a little less attractive – video post jump.
Or you can just use candles.
Extend Your Own Sensor Bar [AVSForum]