Thanks to JaremyP for the inspiration. See his DC adapter hack thread here:https://www.avsforum.com/avs-vb/showthread.php?t=754430
We have a front projection system, and last night (first with the Wii) we had everything in the open (rather than in the media rack custom built for the room) due to this sensor bar issue. While it worked fine, it was inelegant, at best, and I needed a better solution.
I was hoping I could get Jaremy's fix to work, but I was unsuccessful, as he was at first, with an old universal adapter (set to 7.5V) that I found around the house. It's possible that my adapter was shot (I didn't test it with another appliance before snipping its wire) or my soldering was poor.
So to try and achieve something a little better (and not requiring soldering the tiny little wires) I went to "the Shack" this evening and bought:
1. A five-pack of 9V Battery Snap Connectors (~$1.99) part 270-325
2. A pack (24) of insulated telephone "Butt connectors" for 22-26 gauge wire (part #64-3073). No, I'm not joking--that is what they're called. They are basically a small cylinder surrounded by an insulated sheath. You stick a bare wire in each end, and then crimp the middle.
3. One 9V battery
I proceeded to strip the wires as in Jaremy's post, and simply crimped the battery connector wires to the sensor bar wires using the butt connectors (red from the battery connector from the Wii sensor bar red wire, and black from the battery connector to orange from the sensor bar).
I did a quick test with my old sensor bar unplugged, and it seems to be working perfectly. One disclaimer--I haven't tested this for any lengthy period, yet. I would also suggest that you do this with a replacement sensor bar rather than your original(they're in stock shipping straight from Nintendo, for $10).